diff --git a/composer.json b/composer.json
index c7080d8..8e6bb51 100644
--- a/composer.json
+++ b/composer.json
@@ -4,7 +4,7 @@
     "type": "project",
     "license": "GPLv3",
     "require": {
-        "convertkit/convertkit-wordpress-libraries": "2.1.2"
+        "convertkit/convertkit-wordpress-libraries": "dev-add-invalid-access-token-to-hook"
     },
     "require-dev": {
         "php-webdriver/webdriver": "^1.0",
diff --git a/includes/class-integrate-convertkit-wpforms-admin-notices.php b/includes/class-integrate-convertkit-wpforms-admin-notices.php
new file mode 100644
index 0000000..fcbe274
--- /dev/null
+++ b/includes/class-integrate-convertkit-wpforms-admin-notices.php
@@ -0,0 +1,223 @@
+<?php
+/**
+ * ConvertKit WPForms Admin Notices class.
+ *
+ * @package ConvertKit_WPForms
+ * @author ConvertKit
+ */
+
+/**
+ * Add and remove persistent error messages across all
+ * WordPress Administration screens.
+ *
+ * @package ConvertKit_WPForms
+ * @author ConvertKit
+ */
+class Integrate_ConvertKit_WPForms_Admin_Notices {
+
+	/**
+	 * Holds the class object.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @var     object
+	 */
+	private static $instance;
+
+	/**
+	 * The key prefix to use for stored notices
+	 *
+	 * @since   1.8.9
+	 *
+	 * @var     string
+	 */
+	private $key_prefix = 'integrate-convertkit-wpforms-admin-notices';
+
+	/**
+	 * Register output function to display persistent notices
+	 * in the WordPress Administration, if any exist.
+	 *
+	 * @since   1.8.9
+	 */
+	public function __construct() {
+
+		add_action( 'admin_notices', array( $this, 'output' ) );
+
+	}
+
+	/**
+	 * Output persistent notices in the WordPress Administration
+	 *
+	 * @since   1.8.9
+	 */
+	public function output() {
+
+		// Don't output if we don't have the required capabilities to fix the issue.
+		if ( ! current_user_can( 'manage_options' ) ) {
+			return;
+		}
+
+		// Bail if no notices exist.
+		$notices = get_option( $this->key_prefix );
+		if ( ! $notices ) {
+			return;
+		}
+
+		// Output notices.
+		foreach ( $notices as $notice ) {
+			switch ( $notice ) {
+				case 'authorization_failed':
+					$output = sprintf(
+						'%s %s',
+						esc_html__( 'Kit for WPForms: Authorization failed. Please', 'integrate-convertkit-wpforms' ),
+						sprintf(
+							'<a href="%s">%s</a>',
+							esc_url( admin_url( 'admin.php?page=wpforms-settings&view=integrations' ) ),
+							esc_html__( 'reconnect your Kit account.', 'integrate-convertkit-wpforms' )
+						)
+					);
+					break;
+
+				default:
+					$output = '';
+
+					/**
+					 * Define the text to output in an admin error notice.
+					 *
+					 * @since   1.8.9
+					 *
+					 * @param   string  $notice     Admin notice name.
+					 */
+					$output = apply_filters( 'integrate_convertkit_wpforms_admin_notices_output_' . $notice, $output );
+					break;
+			}
+
+			// If no output defined, skip.
+			if ( empty( $output ) ) {
+				continue;
+			}
+			?>
+			<div class="notice notice-error">
+				<p>
+					<?php
+					echo wp_kses(
+						$output,
+						wp_kses_allowed_html( 'post' )
+					);
+					?>
+				</p>
+			</div>
+			<?php
+		}
+
+	}
+
+	/**
+	 * Add a persistent notice for output in the WordPress Administration.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @param   string $notice     Notice name.
+	 * @return  bool                Notice saved successfully
+	 */
+	public function add( $notice ) {
+
+		// If no other persistent notices exist, add one now.
+		if ( ! $this->exist() ) {
+			return update_option( $this->key_prefix, array( $notice ) );
+		}
+
+		// Fetch existing persistent notices.
+		$notices = $this->get();
+
+		// Add notice to existing notices.
+		$notices[] = $notice;
+
+		// Remove any duplicate notices.
+		$notices = array_values( array_unique( $notices ) );
+
+		// Update and return.
+		return update_option( $this->key_prefix, $notices );
+
+	}
+
+	/**
+	 * Returns all notices stored in the options table.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @return  array
+	 */
+	public function get() {
+
+		// Fetch all notices from the options table.
+		return get_option( $this->key_prefix );
+
+	}
+
+	/**
+	 * Whether any persistent notices are stored in the option table.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @return  bool
+	 */
+	public function exist() {
+
+		if ( ! $this->get() ) {
+			return false;
+		}
+
+		return true;
+
+	}
+
+	/**
+	 * Delete all persistent notices.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @param   string $notice     Notice name.
+	 * @return  bool                Success
+	 */
+	public function delete( $notice ) {
+
+		// If no persistent notices exist, there's nothing to delete.
+		if ( ! $this->exist() ) {
+			return false;
+		}
+
+		// Fetch existing persistent notices.
+		$notices = $this->get();
+
+		// Remove notice from existing notices.
+		$index = array_search( $notice, $notices, true );
+		if ( $index !== false ) {
+			unset( $notices[ $index ] );
+		}
+
+		// Update and return.
+		return update_option( $this->key_prefix, $notices );
+
+	}
+
+	/**
+	 * Returns the singleton instance of the class.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @return  object Class.
+	 */
+	public static function get_instance() {
+
+		if ( null === self::$instance ) {
+			self::$instance = new self();
+		}
+
+		return self::$instance;
+
+	}
+
+}
+
+new Integrate_ConvertKit_WPForms_Admin_Notices();
diff --git a/includes/class-integrate-convertkit-wpforms-api.php b/includes/class-integrate-convertkit-wpforms-api.php
index a766a0e..01c9d30 100644
--- a/includes/class-integrate-convertkit-wpforms-api.php
+++ b/includes/class-integrate-convertkit-wpforms-api.php
@@ -113,4 +113,17 @@ public function __construct( $client_id, $redirect_uri, $access_token = false, $
 
 	}
 
+	/**
+	 * Returns the access token.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @return  string
+	 */
+	public function access_token() {
+
+		return $this->access_token;
+
+	}
+
 }
diff --git a/includes/class-integrate-convertkit-wpforms-resource.php b/includes/class-integrate-convertkit-wpforms-resource.php
index 551b730..91e8b77 100644
--- a/includes/class-integrate-convertkit-wpforms-resource.php
+++ b/includes/class-integrate-convertkit-wpforms-resource.php
@@ -14,6 +14,13 @@
  */
 class Integrate_ConvertKit_WPForms_Resource extends ConvertKit_Resource_V4 {
 
+	/**
+	 * The API class
+	 *
+	 * @var     bool|Integrate_ConvertKit_WPForms_API
+	 */
+	public $api = false;
+
 	/**
 	 * Constructor.
 	 *
@@ -33,8 +40,34 @@ public function __construct( $api_instance, $account_id = '' ) {
 			$this->settings_name .= '_' . $account_id;
 		}
 
-		// Call parent initialization function.
-		parent::init();
+		// Get last query time and existing resources.
+		$this->last_queried = get_option( $this->settings_name . '_last_queried' );
+		$this->resources    = get_option( $this->settings_name );
+
+	}
+
+	/**
+	 * Fetches resources (custom fields, forms, sequences or tags) from the API, storing them in the options table
+	 * with a last queried timestamp.
+	 *
+	 * If the refresh results in a 401, removes the access and refresh tokens from the connection.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @return  WP_Error|array
+	 */
+	public function refresh() {
+
+		// Call parent refresh method.
+		$result = parent::refresh();
+
+		// If an error occured, maybe delete credentials from the Plugin's settings
+		// if the error is a 401 unauthorized.
+		if ( is_wp_error( $result ) ) {
+			integrate_convertkit_wpforms_maybe_delete_credentials( $result, INTEGRATE_CONVERTKIT_WPFORMS_OAUTH_CLIENT_ID, $this->api->access_token() );
+		}
+
+		return $result;
 
 	}
 
diff --git a/includes/class-integrate-convertkit-wpforms.php b/includes/class-integrate-convertkit-wpforms.php
index cc0e54b..b87e7e1 100644
--- a/includes/class-integrate-convertkit-wpforms.php
+++ b/includes/class-integrate-convertkit-wpforms.php
@@ -667,8 +667,8 @@ public function output_accounts( $connection_id = '', $connection = array() ) {
 	}
 
 	/**
-	 * Outputs a <select> dropdown of ConvertKit Forms, allowing the user
-	 * to choose which ConvertKit Form to send form submissions to.
+	 * Outputs a <select> dropdown of Kit Forms, Sequences and Tags, allowing the user
+	 * to choose which resource to send form submissions to.
 	 *
 	 * @since   1.5.0
 	 *
@@ -691,28 +691,67 @@ public function output_lists( $connection_id = '', $connection = array() ) {
 			return '';
 		}
 
+		// Get the selected ConvertKit subscribe setting, if one was already defined.
+		$value = ! empty( $connection['list_id'] ) ? $connection['list_id'] : '';
+
+		// Initialize resource classes.
+		$forms     = new Integrate_ConvertKit_WPForms_Resource_Forms( $api, $connection['account_id'] );
+		$sequences = new Integrate_ConvertKit_WPForms_Resource_Sequences( $api, $connection['account_id'] );
+		$tags      = new Integrate_ConvertKit_WPForms_Resource_Tags( $api, $connection['account_id'] );
+
 		// Fetch Forms.
 		// We use refresh() to ensure we get the latest data, as we're in the admin interface
 		// and need to populate the select dropdown.
-		$forms = new Integrate_ConvertKit_WPForms_Resource_Forms( $api, $connection['account_id'] );
-		$forms->refresh();
+		$result = $forms->refresh();
+
+		// Return the <select> dropdown if an error occurred, so the cached resources are
+		// available for selection.
+		if ( is_wp_error( $result ) ) {
+			return $this->output_select_dropdown( $forms, $sequences, $tags, $value, $connection_id, $result->get_error_message() );
+		}
 
 		// Fetch Sequences.
 		// We use refresh() to ensure we get the latest data, as we're in the admin interface
 		// and need to populate the select dropdown.
-		$sequences = new Integrate_ConvertKit_WPForms_Resource_Sequences( $api, $connection['account_id'] );
-		$sequences->refresh();
+		$result = $sequences->refresh();
+
+		// Return the <select> dropdown if an error occurred, so the cached resources are
+		// available for selection.
+		if ( is_wp_error( $result ) ) {
+			return $this->output_select_dropdown( $forms, $sequences, $tags, $value, $connection_id, $result->get_error_message() );
+		}
 
 		// Fetch Tags.
 		// We use refresh() to ensure we get the latest data, as we're in the admin interface
 		// and need to populate the select dropdown.
-		$tags = new Integrate_ConvertKit_WPForms_Resource_Tags( $api, $connection['account_id'] );
-		$tags->refresh();
+		$result = $tags->refresh();
 
-		// Get the selected ConvertKit subscribe setting, if one was already defined.
-		$value = ! empty( $connection['list_id'] ) ? $connection['list_id'] : '';
+		// Return the <select> dropdown if an error occurred, so the cached resources are
+		// available for selection.
+		if ( is_wp_error( $result ) ) {
+			return $this->output_select_dropdown( $forms, $sequences, $tags, $value, $connection_id, $result->get_error_message() );
+		}
 
 		// Output <select> dropdown.
+		return $this->output_select_dropdown( $forms, $sequences, $tags, $value, $connection_id );
+
+	}
+
+	/**
+	 * Outputs the <select> dropdown.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @param   Integrate_ConvertKit_WPForms_Resource_Forms     $forms         Forms resource.
+	 * @param   Integrate_ConvertKit_WPForms_Resource_Sequences $sequences     Sequences resource.
+	 * @param   Integrate_ConvertKit_WPForms_Resource_Tags      $tags          Tags resource.
+	 * @param   string                                          $value         Selected value.
+	 * @param   string                                          $connection_id Connection ID.
+	 * @param   string                                          $error_message Error message.
+	 * @return  string
+	 */
+	private function output_select_dropdown( $forms, $sequences, $tags, $value, $connection_id, $error_message = '' ) {
+
 		ob_start();
 		require INTEGRATE_CONVERTKIT_WPFORMS_PATH . '/views/backend/settings-form-marketing-forms-dropdown.php';
 		return ob_get_clean();
@@ -871,6 +910,10 @@ public function maybe_get_and_store_access_token() {
 			)
 		);
 
+		// Remove any existing persistent notice.
+		$admin_notices = Integrate_ConvertKit_WPForms_Admin_Notices::get_instance();
+		$admin_notices->delete( 'authorization_failed' );
+
 		// If this request is served in a popup window (i.e. from the form builder),
 		// serve a view that will close the popup.
 		if ( array_key_exists( 'convertkit-modal', $_REQUEST ) ) { // phpcs:ignore WordPress.Security.NonceVerification.Recommended
@@ -974,6 +1017,11 @@ public function api_fields( $connection_id = '', $account_id = '', $list_id = ''
 		$resource_custom_fields = new Integrate_ConvertKit_WPForms_Resource_Custom_Fields( $api, $account_id );
 		$custom_fields          = $resource_custom_fields->refresh();
 
+		// Just return fields if an error occurred.
+		if ( is_wp_error( $custom_fields ) ) {
+			return $provider_fields;
+		}
+
 		// Just return fields if no custom fields exist in ConvertKit.
 		if ( ! count( $custom_fields ) ) {
 			return $provider_fields;
diff --git a/includes/functions.php b/includes/functions.php
index e2a3082..e322f5c 100644
--- a/includes/functions.php
+++ b/includes/functions.php
@@ -16,7 +16,7 @@
  * @param   string $client_id               OAuth Client ID used for the Access and Refresh Tokens.
  * @param   string $previous_access_token   Existing (expired) Access Token.
  */
-function integrate_convertkit_wpforms_update_credentials( $result, $client_id, $previous_access_token = '' ) {
+function integrate_convertkit_wpforms_maybe_update_credentials( $result, $client_id, $previous_access_token = '' ) {
 
 	// Don't save these credentials if they're not for this Client ID.
 	// They're for another ConvertKit Plugin that uses OAuth.
@@ -69,6 +69,79 @@ function integrate_convertkit_wpforms_update_credentials( $result, $client_id, $
 			)
 		);
 
+		// Remove any existing persistent notice.
+		$admin_notices = Integrate_ConvertKit_WPForms_Admin_Notices::get_instance();
+		$admin_notices->delete( 'authorization_failed' );
+
+		// Break out of the loop now the credentials have been updated.
+		break;
+	}
+
+}
+
+/**
+ * Deletes the stored access token, refresh token and its expiry from the Plugin settings,
+ * and clears any existing scheduled WordPress Cron event to refresh the token on expiry,
+ * when either:
+ * - The access token is invalid
+ * - The access token expired, and refreshing failed
+ *
+ * @since   1.8.9
+ *
+ * @param   WP_Error $result                  Error result.
+ * @param   string   $client_id               OAuth Client ID used for the Access and Refresh Tokens.
+ * @param   string   $invalid_access_token    Existing (invalid) Access Token.
+ */
+function integrate_convertkit_wpforms_maybe_delete_credentials( $result, $client_id, $invalid_access_token = '' ) {
+
+	// Don't save these credentials if they're not for this Client ID.
+	// They're for another ConvertKit Plugin that uses OAuth.
+	if ( $client_id !== INTEGRATE_CONVERTKIT_WPFORMS_OAUTH_CLIENT_ID ) {
+		return;
+	}
+
+	// Get all registered providers in WPForms.
+	$providers = wpforms_get_providers_options();
+
+	// Bail if no ConvertKit providers were registered.
+	if ( ! array_key_exists( 'convertkit', $providers ) ) {
+		return;
+	}
+
+	// Iterate through providers to find the specific connection containing the now invalid Access Token.
+	foreach ( $providers['convertkit'] as $id => $settings ) {
+		// Skip if this isn't the connection.
+		if ( $settings['access_token'] !== $invalid_access_token ) {
+			continue;
+		}
+
+		// Persist an error notice in the WordPress Administration until the user fixes the problem.
+		$admin_notices = Integrate_ConvertKit_WPForms_Admin_Notices::get_instance();
+		$admin_notices->add( 'authorization_failed' );
+
+		// Remove the invalid tokens from the connection.
+		// Keep the connection so the user doesn't lose settings on WPForms Forms.
+		// They can use the Reconnect link at WPForms > Settings > Integrations > Kit > Reconnect.
+		wpforms_update_providers_options(
+			'convertkit',
+			array(
+				'access_token'  => '',
+				'refresh_token' => '',
+				'token_expires' => 0,
+				'label'         => $settings['label'],
+				'date'          => time(),
+			),
+			$id
+		);
+
+		// Clear any existing scheduled WordPress Cron event for this connection.
+		wp_clear_scheduled_hook(
+			'integrate_convertkit_wpforms_refresh_token',
+			array(
+				$id,
+			)
+		);
+
 		// Break out of the loop now the credentials have been updated.
 		break;
 	}
@@ -76,4 +149,8 @@ function integrate_convertkit_wpforms_update_credentials( $result, $client_id, $
 }
 
 // Update Access Token when refreshed by the API class.
-add_action( 'convertkit_api_refresh_token', 'integrate_convertkit_wpforms_update_credentials', 10, 3 );
+add_action( 'convertkit_api_refresh_token', 'integrate_convertkit_wpforms_maybe_update_credentials', 10, 3 );
+
+// Delete credentials if the API class uses a invalid access token.
+// This prevents the Plugin making repetitive API requests that will 401.
+add_action( 'convertkit_api_access_token_invalid', 'integrate_convertkit_wpforms_maybe_delete_credentials', 10, 3 );
diff --git a/integrate-convertkit-wpforms.php b/integrate-convertkit-wpforms.php
index cf3b281..aea6f88 100644
--- a/integrate-convertkit-wpforms.php
+++ b/integrate-convertkit-wpforms.php
@@ -50,6 +50,7 @@
 }
 
 // Load required functions.
+require_once INTEGRATE_CONVERTKIT_WPFORMS_PATH . '/includes/class-integrate-convertkit-wpforms-admin-notices.php';
 require_once INTEGRATE_CONVERTKIT_WPFORMS_PATH . '/includes/functions.php';
 require_once INTEGRATE_CONVERTKIT_WPFORMS_PATH . '/includes/cron-functions.php';
 
diff --git a/tests/EndToEnd.suite.yml b/tests/EndToEnd.suite.yml
index 07bcc91..bce6fb9 100644
--- a/tests/EndToEnd.suite.yml
+++ b/tests/EndToEnd.suite.yml
@@ -25,6 +25,7 @@ modules:
         - \Tests\Support\Helper\Plugin
         - \Tests\Support\Helper\ThirdPartyPlugin
         - \Tests\Support\Helper\WPForms
+        - \Tests\Support\Helper\WPNotices
         - \Tests\Support\Helper\Xdebug
     config:
         lucatume\WPBrowser\Module\WPWebDriver:
@@ -40,7 +41,6 @@ modules:
             capabilities:
               "goog:chromeOptions":
                 args:
-                  - "--headless"
                   - "--disable-gpu"
                   - "--disable-dev-shm-usage"
                   - "--disable-software-rasterizer"
diff --git a/tests/EndToEnd/general/IntegrationsCest.php b/tests/EndToEnd/general/IntegrationsCest.php
index a6733c9..08858f6 100644
--- a/tests/EndToEnd/general/IntegrationsCest.php
+++ b/tests/EndToEnd/general/IntegrationsCest.php
@@ -126,6 +126,58 @@ public function testAddIntegrationWithInvalidAPICredentials(EndToEndTester $I)
 		$I->see($errorDescription);
 	}
 
+	/**
+	 * Test that an error notification is displayed when the API credentials are invalid.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @param   EndToEndTester $I  Tester.
+	 */
+	public function testInvalidCredentials(EndToEndTester $I)
+	{
+		// Define connection with invalid API credentials.
+		$I->setupWPFormsIntegration(
+			$I,
+			'fakeAccessToken',
+			'fakeRefreshToken'
+		);
+
+		// Setup WPForms Form and configuration for this test.
+		// Create Form.
+		$wpFormsID = $I->createWPFormsForm($I);
+
+		// Load WPForms Editor.
+		$I->amOnAdminPage('admin.php?page=wpforms-builder&view=fields&form_id=' . $wpFormsID);
+
+		// Click Marketing icon.
+		$I->waitForElementVisible('.wpforms-panel-providers-button');
+		$I->click('.wpforms-panel-providers-button');
+
+		// Click ConvertKit tab.
+		$I->click('#wpforms-panel-providers a.wpforms-panel-sidebar-section-convertkit');
+
+		// Click Add New Connection.
+		$I->click('Add New Connection');
+
+		// Define name for connection.
+		$I->waitForElementVisible('.jconfirm-content');
+		$I->fillField('#provider-connection-name', 'Kit');
+		$I->click('OK');
+
+		// Get the connection ID.
+		$I->waitForElementVisible('.wpforms-provider-connections .wpforms-provider-connection');
+		$connectionID = $I->grabAttributeFrom('.wpforms-provider-connections .wpforms-provider-connection', 'data-connection_id');
+
+		// Specify field values.
+		$I->waitForElementVisible('div[data-connection_id="' . $connectionID . '"] .wpforms-provider-fields', 30);
+
+		// Navigate to the WordPress Admin.
+		$I->amOnAdminPage('index.php');
+
+		// Check that a notice is displayed that the API credentials are invalid.
+		$I->seeErrorNotice($I, 'Kit for WPForms: Authorization failed. Please reconnect your Kit account.');
+	}
+
 	/**
 	 * Deactivate and reset Plugin(s) after each test, if the test passes.
 	 * We don't use _after, as this would provide a screenshot of the Plugin
diff --git a/tests/Integration/APITest.php b/tests/Integration/APITest.php
index a2c3e7a..81ab917 100644
--- a/tests/Integration/APITest.php
+++ b/tests/Integration/APITest.php
@@ -110,6 +110,56 @@ public function testAccessTokenRefreshedAndSavedWhenExpired()
 		$this->assertEquals($_ENV['CONVERTKIT_OAUTH_REFRESH_TOKEN'], $account['refresh_token']);
 	}
 
+	/**
+	 * Test that the Access Token, Refresh Token and Token Expiry are deleted from the Plugin's settings
+	 * when the Access Token used is invalid.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testAccessTokenDeletedWhenInvalid()
+	{
+		// Save an invalid access token and refresh token in the Plugin's settings.
+		wpforms_update_providers_options(
+			'convertkit',
+			array(
+				'access_token'  => 'invalidAccessToken',
+				'refresh_token' => $_ENV['CONVERTKIT_OAUTH_REFRESH_TOKEN'],
+				'token_expires' => time() + 10000,
+				'label'         => 'ConvertKit WordPress',
+				'date'          => time(),
+			),
+			'wpunittest1234'
+		);
+
+		// Confirm the tokens saved.
+		$providers = wpforms_get_providers_options();
+		$account   = reset( $providers['convertkit'] );
+		$this->assertEquals( $account['access_token'], 'invalidAccessToken' );
+		$this->assertEquals( $account['refresh_token'], $_ENV['CONVERTKIT_OAUTH_REFRESH_TOKEN'] );
+
+		// Initialize the API using the invalid access token.
+		$api = new \Integrate_ConvertKit_WPForms_API(
+			$_ENV['CONVERTKIT_OAUTH_CLIENT_ID'],
+			$_ENV['KIT_OAUTH_REDIRECT_URI'],
+			$account['access_token'],
+			$account['refresh_token']
+		);
+
+		// Run request.
+		$result = $api->get_account();
+
+		// Confirm a WP_Error is returned.
+		$this->assertInstanceOf( 'WP_Error', $result );
+		$this->assertEquals( $result->get_error_code(), 'convertkit_api_error' );
+		$this->assertEquals( $result->get_error_message(), 'The access token is invalid' );
+
+		// Confirm tokens removed from the Plugin's settings, which confirms the `convertkit_api_access_token_invalid` hook was called when the tokens were deleted.
+		$providers = wpforms_get_providers_options();
+		$account   = reset( $providers['convertkit'] );
+		$this->assertEmpty( $account['access_token'] );
+		$this->assertEmpty( $account['refresh_token'] );
+	}
+
 	/**
 	 * Test that a WordPress Cron event is created when an access token is obtained.
 	 *
diff --git a/tests/Integration/ResourceCustomFieldsNoDataTest.php b/tests/Integration/ResourceCustomFieldsNoDataTest.php
new file mode 100644
index 0000000..0b7be03
--- /dev/null
+++ b/tests/Integration/ResourceCustomFieldsNoDataTest.php
@@ -0,0 +1,196 @@
+<?php
+
+namespace Tests;
+
+use lucatume\WPBrowser\TestCase\WPTestCase;
+
+/**
+ * Tests for the Integrate_ConvertKit_WPForms_Resource_Custom_Fields class when no data is present in the API.
+ *
+ * @since   1.8.9
+ */
+class ResourceCustomFieldsNoDataTest extends \Codeception\TestCase\WPTestCase
+{
+	/**
+	 * The testing implementation.
+	 *
+	 * @var \WpunitTester
+	 */
+	protected $tester;
+
+	/**
+	 * Holds the API instance.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @var     Integrate_ConvertKit_WPForms_API
+	 */
+	private $api;
+
+	/**
+	 * Holds the ConvertKit Resource class.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @var     Integrate_ConvertKit_WPForms_Resource_Custom_Fields
+	 */
+	private $resource;
+
+	/**
+	 * Holds the WPForms Account ID to store the Access Token and Refresh Token in WPForms's settings.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @var     string
+	 */
+	protected $wpforms_account_id = 'kit-unit-test';
+
+	/**
+	 * Performs actions before each test.
+	 *
+	 * @since   1.8.9
+	 */
+	public function setUp(): void
+	{
+		parent::setUp();
+
+		// Activate Plugin, to include the Plugin's constants in tests.
+		activate_plugins('wpforms-lite/wpforms.php');
+		activate_plugins('convertkit-wpforms/integrate-convertkit-wpforms.php');
+
+		// Include classes from /includes to test, as they won't be loaded by the Plugin
+		// because WPForms is not active.
+		require_once 'includes/class-integrate-convertkit-wpforms-api.php';
+		require_once 'includes/class-integrate-convertkit-wpforms-resource-custom-fields.php';
+
+		// Storing Access Token and Refresh Token in WPForms's settings.
+		wpforms_update_providers_options(
+			'convertkit',
+			array(
+				'access_token'  => $_ENV['CONVERTKIT_OAUTH_ACCESS_TOKEN_NO_DATA'],
+				'refresh_token' => $_ENV['CONVERTKIT_OAUTH_REFRESH_TOKEN_NO_DATA'],
+				'token_expires' => time() + 10000,
+				'label'         => 'ConvertKit WordPress',
+				'date'          => time(),
+			),
+			$this->wpforms_account_id
+		);
+
+		// Initialize the API instance.
+		$this->api = new \Integrate_ConvertKit_WPForms_API(
+			$_ENV['CONVERTKIT_OAUTH_CLIENT_ID'],
+			$_ENV['CONVERTKIT_OAUTH_REDIRECT_URI'],
+			$_ENV['CONVERTKIT_OAUTH_ACCESS_TOKEN_NO_DATA'],
+			$_ENV['CONVERTKIT_OAUTH_REFRESH_TOKEN_NO_DATA']
+		);
+
+		// Initialize the resource class we want to test with the API instance and WPForms Account ID.
+		$this->resource = new \Integrate_ConvertKit_WPForms_Resource_Custom_Fields( $this->api, $this->wpforms_account_id );
+		$this->assertNotInstanceOf(\WP_Error::class, $this->resource->resources);
+
+		// Initialize the resource class, fetching resources from the API and caching them in the options table.
+		$result = $this->resource->init();
+
+		// Confirm calling init() didn't result in an error.
+		$this->assertNotInstanceOf(\WP_Error::class, $result);
+	}
+
+	/**
+	 * Performs actions after each test.
+	 *
+	 * @since   1.8.9
+	 */
+	public function tearDown(): void
+	{
+		// Disable integration, removing Access Token and Refresh Token from Plugin's settings.
+		wpforms_update_providers_options(
+			'convertkit',
+			array(
+				'access_token'  => '',
+				'refresh_token' => '',
+				'token_expires' => 0,
+				'label'         => 'ConvertKit WordPress',
+				'date'          => time(),
+			),
+			$this->wpforms_account_id
+		);
+
+		// Delete Resources from options table.
+		delete_option($this->resource->settings_name . '_' . $this->wpforms_account_id);
+		delete_option($this->resource->settings_name . '_' . $this->wpforms_account_id . '_last_queried');
+
+		// Destroy the classes we tested.
+		unset($this->api);
+		unset($this->resource);
+
+		parent::tearDown();
+	}
+
+	/**
+	 * Test that the refresh() function performs as expected.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testRefresh()
+	{
+		// Confirm that no resources exist in the stored options table data.
+		$result = $this->resource->refresh();
+		$this->assertNotInstanceOf(\WP_Error::class, $result);
+		$this->assertIsArray($result);
+		$this->assertCount(0, $result);
+	}
+
+	/**
+	 * Test that the expiry timestamp is set and returns the expected value.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testExpiry()
+	{
+		// Define the expected expiry date based on the resource class' $cache_duration setting.
+		$expectedExpiryDate = date('Y-m-d', time() + $this->resource->cache_duration);
+
+		// Fetch the actual expiry date set when the resource class was initialized.
+		$expiryDate = date('Y-m-d', $this->resource->last_queried + $this->resource->cache_duration);
+
+		// Confirm both dates match.
+		$this->assertEquals($expectedExpiryDate, $expiryDate);
+	}
+
+	/**
+	 * Test that the get() function performs as expected.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testGet()
+	{
+		// Confirm that no resources exist in the stored options table data.
+		$result = $this->resource->get();
+		$this->assertNotInstanceOf(\WP_Error::class, $result);
+		$this->assertIsArray($result);
+		$this->assertCount(0, $result);
+	}
+
+	/**
+	 * Test that the count() function returns the number of resources.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testCount()
+	{
+		$result = $this->resource->get();
+		$this->assertEquals($this->resource->count(), count($result));
+	}
+
+	/**
+	 * Test that the exist() function performs as expected.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testExist()
+	{
+		// Confirm that the function returns false, because resources do not exist.
+		$result = $this->resource->exist();
+		$this->assertSame($result, false);
+	}
+}
diff --git a/tests/Integration/ResourceCustomFieldsTest.php b/tests/Integration/ResourceCustomFieldsTest.php
new file mode 100644
index 0000000..30e7dad
--- /dev/null
+++ b/tests/Integration/ResourceCustomFieldsTest.php
@@ -0,0 +1,276 @@
+<?php
+
+namespace Tests;
+
+use lucatume\WPBrowser\TestCase\WPTestCase;
+
+/**
+ * Tests for the Integrate_ConvertKit_WPForms_Resource_Custom_Fields class when data is present in the API.
+ *
+ * @since   1.8.9
+ */
+class ResourceCustomFieldsTest extends \Codeception\TestCase\WPTestCase
+{
+	/**
+	 * The testing implementation.
+	 *
+	 * @var \WpunitTester
+	 */
+	protected $tester;
+
+	/**
+	 * Holds the API instance.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @var     Integrate_ConvertKit_WPForms_API
+	 */
+	private $api;
+
+	/**
+	 * Holds the ConvertKit Resource class.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @var     Integrate_ConvertKit_WPForms_Resource_Custom_Fields
+	 */
+	private $resource;
+
+	/**
+	 * Holds the WPForms Account ID to store the Access Token and Refresh Token in WPForms's settings.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @var     string
+	 */
+	protected $wpforms_account_id = 'kit-unit-test';
+
+	/**
+	 * Performs actions before each test.
+	 *
+	 * @since   1.8.9
+	 */
+	public function setUp(): void
+	{
+		parent::setUp();
+
+		// Activate Plugin, to include the Plugin's constants in tests.
+		activate_plugins('wpforms-lite/wpforms.php');
+		activate_plugins('convertkit-wpforms/integrate-convertkit-wpforms.php');
+
+		// Include classes from /includes to test, as they won't be loaded by the Plugin
+		// because WPForms is not active.
+		require_once 'includes/class-integrate-convertkit-wpforms-api.php';
+		require_once 'includes/class-integrate-convertkit-wpforms-resource-custom-fields.php';
+
+		// Storing Access Token and Refresh Token in WPForms's settings.
+		wpforms_update_providers_options(
+			'convertkit',
+			array(
+				'access_token'  => $_ENV['CONVERTKIT_OAUTH_ACCESS_TOKEN'],
+				'refresh_token' => $_ENV['CONVERTKIT_OAUTH_REFRESH_TOKEN'],
+				'token_expires' => time() + 10000,
+				'label'         => 'ConvertKit WordPress',
+				'date'          => time(),
+			),
+			$this->wpforms_account_id
+		);
+
+		// Initialize the API instance.
+		$this->api = new \Integrate_ConvertKit_WPForms_API(
+			$_ENV['CONVERTKIT_OAUTH_CLIENT_ID'],
+			$_ENV['CONVERTKIT_OAUTH_REDIRECT_URI'],
+			$_ENV['CONVERTKIT_OAUTH_ACCESS_TOKEN'],
+			$_ENV['CONVERTKIT_OAUTH_REFRESH_TOKEN']
+		);
+
+		// Initialize the resource class we want to test with the API instance and WPForms Account ID.
+		$this->resource = new \Integrate_ConvertKit_WPForms_Resource_Custom_Fields( $this->api, $this->wpforms_account_id );
+		$this->assertNotInstanceOf(\WP_Error::class, $this->resource->resources);
+
+		// Initialize the resource class, fetching resources from the API and caching them in the options table.
+		$result = $this->resource->init();
+
+		// Confirm calling init() didn't result in an error.
+		$this->assertNotInstanceOf(\WP_Error::class, $result);
+	}
+
+	/**
+	 * Performs actions after each test.
+	 *
+	 * @since   1.8.9
+	 */
+	public function tearDown(): void
+	{
+		// Disable integration, removing Access Token and Refresh Token from Plugin's settings.
+		wpforms_update_providers_options(
+			'convertkit',
+			array(
+				'access_token'  => '',
+				'refresh_token' => '',
+				'token_expires' => 0,
+				'label'         => 'ConvertKit WordPress',
+				'date'          => time(),
+			),
+			$this->wpforms_account_id
+		);
+
+		// Delete Resources from options table.
+		delete_option($this->resource->settings_name . '_' . $this->wpforms_account_id);
+		delete_option($this->resource->settings_name . '_' . $this->wpforms_account_id . '_last_queried');
+
+		// Destroy the classes we tested.
+		unset($this->api);
+		unset($this->resource);
+
+		parent::tearDown();
+	}
+
+	/**
+	 * Test that the refresh() function performs as expected.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testRefresh()
+	{
+		// Confirm that the data is stored in the options table and includes some expected keys.
+		$result = $this->resource->refresh();
+		$this->assertIsArray($result);
+		$this->assertArrayHasKey('id', reset($result));
+		$this->assertArrayHasKey('name', reset($result));
+	}
+
+	/**
+	 * Test that the expiry timestamp is set and returns the expected value.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testExpiry()
+	{
+		// Define the expected expiry date based on the resource class' $cache_duration setting.
+		$expectedExpiryDate = date('Y-m-d', time() + $this->resource->cache_duration);
+
+		// Fetch the actual expiry date set when the resource class was initialized.
+		$expiryDate = date('Y-m-d', $this->resource->last_queried + $this->resource->cache_duration);
+
+		// Confirm both dates match.
+		$this->assertEquals($expectedExpiryDate, $expiryDate);
+	}
+
+	/**
+	 * Tests that the get() function returns resources in alphabetical ascending order
+	 * by default.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testGet()
+	{
+		// Call resource class' get() function.
+		$result = $this->resource->get();
+
+		// Assert result is an array.
+		$this->assertIsArray($result);
+
+		// Assert top level array keys are preserved.
+		$this->assertArrayHasKey(array_key_first($this->resource->resources), $result);
+		$this->assertArrayHasKey(array_key_last($this->resource->resources), $result);
+
+		// Assert resource within results has expected array keys.
+		$this->assertArrayHasKey('id', reset($result));
+		$this->assertArrayHasKey('name', reset($result));
+		$this->assertArrayHasKey('key', reset($result));
+		$this->assertArrayHasKey('label', reset($result));
+
+		// Assert order of data is in ascending alphabetical order.
+		$this->assertEquals('Billing Address', reset($result)[ $this->resource->order_by ]);
+		$this->assertEquals('URL', end($result)[ $this->resource->order_by ]);
+	}
+
+	/**
+	 * Tests that the get() function returns resources in alphabetical descending order
+	 * when a valid order_by and order properties are defined.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testGetWithValidOrderByAndOrder()
+	{
+		// Define order_by and order.
+		$this->resource->order_by = 'key';
+		$this->resource->order    = 'desc';
+
+		// Call resource class' get() function.
+		$result = $this->resource->get();
+
+		// Assert result is an array.
+		$this->assertIsArray($result);
+
+		// Assert top level array keys are preserved.
+		$this->assertArrayHasKey(array_key_first($this->resource->resources), $result);
+		$this->assertArrayHasKey(array_key_last($this->resource->resources), $result);
+
+		// Assert resource within results has expected array keys.
+		$this->assertArrayHasKey('id', reset($result));
+		$this->assertArrayHasKey('name', reset($result));
+		$this->assertArrayHasKey('key', reset($result));
+		$this->assertArrayHasKey('label', reset($result));
+
+		// Assert order of data is in descending alphabetical order.
+		$this->assertEquals('url', reset($result)[ $this->resource->order_by ]);
+		$this->assertEquals('billing_address', end($result)[ $this->resource->order_by ]);
+	}
+
+	/**
+	 * Tests that the get() function returns resources in their original order
+	 * when populated with Forms and an invalid order_by value is specified.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testGetWithInvalidOrderBy()
+	{
+		// Define order_by with an invalid value (i.e. an array key that does not exist).
+		$this->resource->order_by = 'invalid_key';
+
+		// Call resource class' get() function.
+		$result = $this->resource->get();
+
+		// Assert result is an array.
+		$this->assertIsArray($result);
+
+		// Assert top level array keys are preserved.
+		$this->assertArrayHasKey(array_key_first($this->resource->resources), $result);
+		$this->assertArrayHasKey(array_key_last($this->resource->resources), $result);
+
+		// Assert resource within results has expected array keys.
+		$this->assertArrayHasKey('id', reset($result));
+		$this->assertArrayHasKey('name', reset($result));
+		$this->assertArrayHasKey('key', reset($result));
+		$this->assertArrayHasKey('label', reset($result));
+
+		// Assert order of data has not changed.
+		$this->assertEquals('URL', reset($result)['label']);
+		$this->assertEquals('Notes', end($result)['label']);
+	}
+
+	/**
+	 * Test that the count() function returns the number of resources.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testCount()
+	{
+		$result = $this->resource->get();
+		$this->assertEquals($this->resource->count(), count($result));
+	}
+
+	/**
+	 * Test that the exist() function performs as expected.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testExist()
+	{
+		// Confirm that the function returns true, because resources exist.
+		$result = $this->resource->exist();
+		$this->assertSame($result, true);
+	}
+}
diff --git a/tests/Integration/ResourceFormsNoDataTest.php b/tests/Integration/ResourceFormsNoDataTest.php
new file mode 100644
index 0000000..43dd735
--- /dev/null
+++ b/tests/Integration/ResourceFormsNoDataTest.php
@@ -0,0 +1,196 @@
+<?php
+
+namespace Tests;
+
+use lucatume\WPBrowser\TestCase\WPTestCase;
+
+/**
+ * Tests for the Integrate_ConvertKit_WPForms_Resource_Forms class when no data is present in the API.
+ *
+ * @since   1.8.9
+ */
+class ResourceFormsNoDataTest extends \Codeception\TestCase\WPTestCase
+{
+	/**
+	 * The testing implementation.
+	 *
+	 * @var \WpunitTester
+	 */
+	protected $tester;
+
+	/**
+	 * Holds the API instance.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @var     Integrate_ConvertKit_WPForms_API
+	 */
+	private $api;
+
+	/**
+	 * Holds the ConvertKit Resource class.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @var     Integrate_ConvertKit_WPForms_Resource_Forms
+	 */
+	private $resource;
+
+	/**
+	 * Holds the WPForms Account ID to store the Access Token and Refresh Token in WPForms's settings.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @var     string
+	 */
+	protected $wpforms_account_id = 'kit-unit-test';
+
+	/**
+	 * Performs actions before each test.
+	 *
+	 * @since   1.8.9
+	 */
+	public function setUp(): void
+	{
+		parent::setUp();
+
+		// Activate Plugin, to include the Plugin's constants in tests.
+		activate_plugins('wpforms-lite/wpforms.php');
+		activate_plugins('convertkit-wpforms/integrate-convertkit-wpforms.php');
+
+		// Include classes from /includes to test, as they won't be loaded by the Plugin
+		// because WPForms is not active.
+		require_once 'includes/class-integrate-convertkit-wpforms-api.php';
+		require_once 'includes/class-integrate-convertkit-wpforms-resource-forms.php';
+
+		// Storing Access Token and Refresh Token in WPForms's settings.
+		wpforms_update_providers_options(
+			'convertkit',
+			array(
+				'access_token'  => $_ENV['CONVERTKIT_OAUTH_ACCESS_TOKEN_NO_DATA'],
+				'refresh_token' => $_ENV['CONVERTKIT_OAUTH_REFRESH_TOKEN_NO_DATA'],
+				'token_expires' => time() + 10000,
+				'label'         => 'ConvertKit WordPress',
+				'date'          => time(),
+			),
+			$this->wpforms_account_id
+		);
+
+		// Initialize the API instance.
+		$this->api = new \Integrate_ConvertKit_WPForms_API(
+			$_ENV['CONVERTKIT_OAUTH_CLIENT_ID'],
+			$_ENV['CONVERTKIT_OAUTH_REDIRECT_URI'],
+			$_ENV['CONVERTKIT_OAUTH_ACCESS_TOKEN_NO_DATA'],
+			$_ENV['CONVERTKIT_OAUTH_REFRESH_TOKEN_NO_DATA']
+		);
+
+		// Initialize the resource class we want to test with the API instance and WPForms Account ID.
+		$this->resource = new \Integrate_ConvertKit_WPForms_Resource_Forms( $this->api, $this->wpforms_account_id );
+		$this->assertNotInstanceOf(\WP_Error::class, $this->resource->resources);
+
+		// Initialize the resource class, fetching resources from the API and caching them in the options table.
+		$result = $this->resource->init();
+
+		// Confirm calling init() didn't result in an error.
+		$this->assertNotInstanceOf(\WP_Error::class, $result);
+	}
+
+	/**
+	 * Performs actions after each test.
+	 *
+	 * @since   1.8.9
+	 */
+	public function tearDown(): void
+	{
+		// Disable integration, removing Access Token and Refresh Token from Plugin's settings.
+		wpforms_update_providers_options(
+			'convertkit',
+			array(
+				'access_token'  => '',
+				'refresh_token' => '',
+				'token_expires' => 0,
+				'label'         => 'ConvertKit WordPress',
+				'date'          => time(),
+			),
+			$this->wpforms_account_id
+		);
+
+		// Delete Resources from options table.
+		delete_option($this->resource->settings_name . '_' . $this->wpforms_account_id);
+		delete_option($this->resource->settings_name . '_' . $this->wpforms_account_id . '_last_queried');
+
+		// Destroy the classes we tested.
+		unset($this->api);
+		unset($this->resource);
+
+		parent::tearDown();
+	}
+
+	/**
+	 * Test that the refresh() function performs as expected.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testRefresh()
+	{
+		// Confirm that no resources exist in the stored options table data.
+		$result = $this->resource->refresh();
+		$this->assertNotInstanceOf(\WP_Error::class, $result);
+		$this->assertIsArray($result);
+		$this->assertCount(0, $result);
+	}
+
+	/**
+	 * Test that the expiry timestamp is set and returns the expected value.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testExpiry()
+	{
+		// Define the expected expiry date based on the resource class' $cache_duration setting.
+		$expectedExpiryDate = date('Y-m-d', time() + $this->resource->cache_duration);
+
+		// Fetch the actual expiry date set when the resource class was initialized.
+		$expiryDate = date('Y-m-d', $this->resource->last_queried + $this->resource->cache_duration);
+
+		// Confirm both dates match.
+		$this->assertEquals($expectedExpiryDate, $expiryDate);
+	}
+
+	/**
+	 * Test that the get() function performs as expected.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testGet()
+	{
+		// Confirm that no resources exist in the stored options table data.
+		$result = $this->resource->get();
+		$this->assertNotInstanceOf(\WP_Error::class, $result);
+		$this->assertIsArray($result);
+		$this->assertCount(0, $result);
+	}
+
+	/**
+	 * Test that the count() function returns the number of resources.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testCount()
+	{
+		$result = $this->resource->get();
+		$this->assertEquals($this->resource->count(), count($result));
+	}
+
+	/**
+	 * Test that the exist() function performs as expected.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testExist()
+	{
+		// Confirm that the function returns false, because no resources exist.
+		$result = $this->resource->exist();
+		$this->assertSame($result, false);
+	}
+}
diff --git a/tests/Integration/ResourceFormsTest.php b/tests/Integration/ResourceFormsTest.php
new file mode 100644
index 0000000..836daaa
--- /dev/null
+++ b/tests/Integration/ResourceFormsTest.php
@@ -0,0 +1,304 @@
+<?php
+
+namespace Tests;
+
+use lucatume\WPBrowser\TestCase\WPTestCase;
+
+/**
+ * Tests for the Integrate_ConvertKit_WPForms_Resource_Forms class when data is present in the API.
+ *
+ * @since   1.8.9
+ */
+class ResourceFormsTest extends \Codeception\TestCase\WPTestCase
+{
+	/**
+	 * The testing implementation.
+	 *
+	 * @var \WpunitTester
+	 */
+	protected $tester;
+
+	/**
+	 * Holds the API instance.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @var     Integrate_ConvertKit_WPForms_API
+	 */
+	private $api;
+
+	/**
+	 * Holds the ConvertKit Resource class.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @var     Integrate_ConvertKit_WPForms_Resource_Forms
+	 */
+	private $resource;
+
+	/**
+	 * Holds the WPForms Account ID to store the Access Token and Refresh Token in WPForms's settings.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @var     string
+	 */
+	protected $wpforms_account_id = 'kit-unit-test';
+
+	/**
+	 * Performs actions before each test.
+	 *
+	 * @since   1.8.9
+	 */
+	public function setUp(): void
+	{
+		parent::setUp();
+
+		// Activate Plugin, to include the Plugin's constants in tests.
+		activate_plugins('wpforms-lite/wpforms.php');
+		activate_plugins('convertkit-wpforms/integrate-convertkit-wpforms.php');
+
+		// Include classes from /includes to test, as they won't be loaded by the Plugin
+		// because WPForms is not active.
+		require_once 'includes/class-integrate-convertkit-wpforms-api.php';
+		require_once 'includes/class-integrate-convertkit-wpforms-resource-forms.php';
+
+		// Storing Access Token and Refresh Token in WPForms's settings.
+		wpforms_update_providers_options(
+			'convertkit',
+			array(
+				'access_token'  => $_ENV['CONVERTKIT_OAUTH_ACCESS_TOKEN'],
+				'refresh_token' => $_ENV['CONVERTKIT_OAUTH_REFRESH_TOKEN'],
+				'token_expires' => time() + 10000,
+				'label'         => 'ConvertKit WordPress',
+				'date'          => time(),
+			),
+			$this->wpforms_account_id
+		);
+
+		// Initialize the API instance.
+		$this->api = new \Integrate_ConvertKit_WPForms_API(
+			$_ENV['CONVERTKIT_OAUTH_CLIENT_ID'],
+			$_ENV['CONVERTKIT_OAUTH_REDIRECT_URI'],
+			$_ENV['CONVERTKIT_OAUTH_ACCESS_TOKEN'],
+			$_ENV['CONVERTKIT_OAUTH_REFRESH_TOKEN']
+		);
+
+		// Initialize the resource class we want to test with the API instance and WPForms Account ID.
+		$this->resource = new \Integrate_ConvertKit_WPForms_Resource_Forms( $this->api, $this->wpforms_account_id );
+		$this->assertNotInstanceOf(\WP_Error::class, $this->resource->resources);
+
+		// Initialize the resource class, fetching resources from the API and caching them in the options table.
+		$result = $this->resource->init();
+
+		// Confirm calling init() didn't result in an error.
+		$this->assertNotInstanceOf(\WP_Error::class, $result);
+	}
+
+	/**
+	 * Performs actions after each test.
+	 *
+	 * @since   1.8.9
+	 */
+	public function tearDown(): void
+	{
+		// Disable integration, removing Access Token and Refresh Token from Plugin's settings.
+		wpforms_update_providers_options(
+			'convertkit',
+			array(
+				'access_token'  => '',
+				'refresh_token' => '',
+				'token_expires' => 0,
+				'label'         => 'ConvertKit WordPress',
+				'date'          => time(),
+			),
+			$this->wpforms_account_id
+		);
+
+		// Delete Resources from options table.
+		delete_option($this->resource->settings_name . '_' . $this->wpforms_account_id);
+		delete_option($this->resource->settings_name . '_' . $this->wpforms_account_id . '_last_queried');
+
+		// Destroy the classes we tested.
+		unset($this->api);
+		unset($this->resource);
+
+		parent::tearDown();
+	}
+
+	/**
+	 * Test that the refresh() function performs as expected.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testRefresh()
+	{
+		// Confirm that the data is stored in the options table and includes some expected keys.
+		$result = $this->resource->refresh();
+		$this->assertIsArray($result);
+		$this->assertArrayHasKey('id', reset($result));
+		$this->assertArrayHasKey('name', reset($result));
+	}
+
+	/**
+	 * Test that the expiry timestamp is set and returns the expected value.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testExpiry()
+	{
+		// Define the expected expiry date based on the resource class' $cache_duration setting.
+		$expectedExpiryDate = date('Y-m-d', time() + $this->resource->cache_duration);
+
+		// Fetch the actual expiry date set when the resource class was initialized.
+		$expiryDate = date('Y-m-d', $this->resource->last_queried + $this->resource->cache_duration);
+
+		// Confirm both dates match.
+		$this->assertEquals($expectedExpiryDate, $expiryDate);
+	}
+
+	/**
+	 * Tests that the get() function returns resources in alphabetical ascending order
+	 * by default.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testGet()
+	{
+		// Call resource class' get() function.
+		$result = $this->resource->get();
+
+		// Assert result is an array.
+		$this->assertIsArray($result);
+
+		// Assert top level array keys are preserved.
+		$this->assertArrayHasKey(array_key_first($this->resource->resources), $result);
+		$this->assertArrayHasKey(array_key_last($this->resource->resources), $result);
+
+		// Assert resource within results has expected array keys.
+		$this->assertArrayHasKey('id', reset($result));
+		$this->assertArrayHasKey('name', reset($result));
+
+		// Assert order of data is in ascending alphabetical order.
+		$this->assertEquals('AAA Test', reset($result)[ $this->resource->order_by ]);
+		$this->assertEquals('WooCommerce Product Form', end($result)[ $this->resource->order_by ]);
+	}
+
+	/**
+	 * Tests that the get() function returns resources in alphabetical descending order
+	 * when a valid order_by and order properties are defined.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testGetWithValidOrderByAndOrder()
+	{
+		// Define order_by and order.
+		$this->resource->order_by = 'name';
+		$this->resource->order    = 'desc';
+
+		// Call resource class' get() function.
+		$result = $this->resource->get();
+
+		// Assert result is an array.
+		$this->assertIsArray($result);
+
+		// Assert top level array keys are preserved.
+		$this->assertArrayHasKey(array_key_first($this->resource->resources), $result);
+		$this->assertArrayHasKey(array_key_last($this->resource->resources), $result);
+
+		// Assert resource within results has expected array keys.
+		$this->assertArrayHasKey('id', reset($result));
+		$this->assertArrayHasKey('name', reset($result));
+
+		// Assert order of data is in descending alphabetical order.
+		$this->assertEquals('WooCommerce Product Form', reset($result)[ $this->resource->order_by ]);
+		$this->assertEquals('AAA Test', end($result)[ $this->resource->order_by ]);
+	}
+
+	/**
+	 * Tests that the get() function returns resources in their original order
+	 * when populated with Forms and an invalid order_by value is specified.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testGetWithInvalidOrderBy()
+	{
+		// Define order_by with an invalid value (i.e. an array key that does not exist).
+		$this->resource->order_by = 'invalid_key';
+
+		// Call resource class' get() function.
+		$result = $this->resource->get();
+
+		// Assert result is an array.
+		$this->assertIsArray($result);
+
+		// Assert top level array keys are preserved.
+		$this->assertArrayHasKey(array_key_first($this->resource->resources), $result);
+		$this->assertArrayHasKey(array_key_last($this->resource->resources), $result);
+
+		// Assert resource within results has expected array keys.
+		$this->assertArrayHasKey('id', reset($result));
+		$this->assertArrayHasKey('name', reset($result));
+
+		// Assert order of data has not changed.
+		$this->assertEquals('WPForms Form', reset($result)['name']);
+		$this->assertEquals('Legacy Form', end($result)['name']);
+	}
+
+	/**
+	 * Test that the count() function returns the number of resources.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testCount()
+	{
+		$result = $this->resource->get();
+		$this->assertEquals($this->resource->count(), count($result));
+	}
+
+	/**
+	 * Test that the exist() function performs as expected.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testExist()
+	{
+		// Confirm that the function returns true, because resources exist.
+		$result = $this->resource->exist();
+		$this->assertSame($result, true);
+	}
+
+
+	/**
+	 * Test that the is_legacy() function returns true for a Legacy Form ID.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testIsLegacyFormWithLegacyFormID()
+	{
+		$this->resource->refresh();
+		$this->assertTrue($this->resource->is_legacy($_ENV['CONVERTKIT_API_LEGACY_FORM_ID']));
+	}
+
+	/**
+	 * Test that the is_legacy() function returns false for a non-Legacy Form ID.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testIsLegacyFormWithFormID()
+	{
+		$this->resource->refresh();
+		$this->assertFalse($this->resource->is_legacy($_ENV['CONVERTKIT_API_FORM_ID']));
+	}
+
+	/**
+	 * Test that the is_legacy() function returns false for an invalid Form ID.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testIsLegacyFormWithInvalidFormID()
+	{
+		$this->resource->refresh();
+		$this->assertFalse($this->resource->is_legacy(12345));
+	}
+}
diff --git a/tests/Integration/ResourceSequencesNoDataTest.php b/tests/Integration/ResourceSequencesNoDataTest.php
new file mode 100644
index 0000000..5a65962
--- /dev/null
+++ b/tests/Integration/ResourceSequencesNoDataTest.php
@@ -0,0 +1,196 @@
+<?php
+
+namespace Tests;
+
+use lucatume\WPBrowser\TestCase\WPTestCase;
+
+/**
+ * Tests for the Integrate_ConvertKit_WPForms_Resource_Sequences class when no data is present in the API.
+ *
+ * @since   1.8.9
+ */
+class ResourceSequencesNoDataTest extends \Codeception\TestCase\WPTestCase
+{
+	/**
+	 * The testing implementation.
+	 *
+	 * @var \WpunitTester
+	 */
+	protected $tester;
+
+	/**
+	 * Holds the API instance.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @var     Integrate_ConvertKit_WPForms_API
+	 */
+	private $api;
+
+	/**
+	 * Holds the ConvertKit Resource class.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @var     Integrate_ConvertKit_WPForms_Resource_Sequences
+	 */
+	private $resource;
+
+	/**
+	 * Holds the WPForms Account ID to store the Access Token and Refresh Token in WPForms's settings.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @var     string
+	 */
+	protected $wpforms_account_id = 'kit-unit-test';
+
+	/**
+	 * Performs actions before each test.
+	 *
+	 * @since   1.8.9
+	 */
+	public function setUp(): void
+	{
+		parent::setUp();
+
+		// Activate Plugin, to include the Plugin's constants in tests.
+		activate_plugins('wpforms-lite/wpforms.php');
+		activate_plugins('convertkit-wpforms/integrate-convertkit-wpforms.php');
+
+		// Include classes from /includes to test, as they won't be loaded by the Plugin
+		// because WPForms is not active.
+		require_once 'includes/class-integrate-convertkit-wpforms-api.php';
+		require_once 'includes/class-integrate-convertkit-wpforms-resource-sequences.php';
+
+		// Storing Access Token and Refresh Token in WPForms's settings.
+		wpforms_update_providers_options(
+			'convertkit',
+			array(
+				'access_token'  => $_ENV['CONVERTKIT_OAUTH_ACCESS_TOKEN_NO_DATA'],
+				'refresh_token' => $_ENV['CONVERTKIT_OAUTH_REFRESH_TOKEN_NO_DATA'],
+				'token_expires' => time() + 10000,
+				'label'         => 'ConvertKit WordPress',
+				'date'          => time(),
+			),
+			$this->wpforms_account_id
+		);
+
+		// Initialize the API instance.
+		$this->api = new \Integrate_ConvertKit_WPForms_API(
+			$_ENV['CONVERTKIT_OAUTH_CLIENT_ID'],
+			$_ENV['CONVERTKIT_OAUTH_REDIRECT_URI'],
+			$_ENV['CONVERTKIT_OAUTH_ACCESS_TOKEN_NO_DATA'],
+			$_ENV['CONVERTKIT_OAUTH_REFRESH_TOKEN_NO_DATA']
+		);
+
+		// Initialize the resource class we want to test with the API instance and WPForms Account ID.
+		$this->resource = new \Integrate_ConvertKit_WPForms_Resource_Sequences( $this->api, $this->wpforms_account_id );
+		$this->assertNotInstanceOf(\WP_Error::class, $this->resource->resources);
+
+		// Initialize the resource class, fetching resources from the API and caching them in the options table.
+		$result = $this->resource->init();
+
+		// Confirm calling init() didn't result in an error.
+		$this->assertNotInstanceOf(\WP_Error::class, $result);
+	}
+
+	/**
+	 * Performs actions after each test.
+	 *
+	 * @since   1.8.9
+	 */
+	public function tearDown(): void
+	{
+		// Disable integration, removing Access Token and Refresh Token from Plugin's settings.
+		wpforms_update_providers_options(
+			'convertkit',
+			array(
+				'access_token'  => '',
+				'refresh_token' => '',
+				'token_expires' => 0,
+				'label'         => 'ConvertKit WordPress',
+				'date'          => time(),
+			),
+			$this->wpforms_account_id
+		);
+
+		// Delete Resources from options table.
+		delete_option($this->resource->settings_name . '_' . $this->wpforms_account_id);
+		delete_option($this->resource->settings_name . '_' . $this->wpforms_account_id . '_last_queried');
+
+		// Destroy the classes we tested.
+		unset($this->api);
+		unset($this->resource);
+
+		parent::tearDown();
+	}
+
+	/**
+	 * Test that the refresh() function performs as expected.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testRefresh()
+	{
+		// Confirm that no resources exist in the stored options table data.
+		$result = $this->resource->refresh();
+		$this->assertNotInstanceOf(\WP_Error::class, $result);
+		$this->assertIsArray($result);
+		$this->assertCount(0, $result);
+	}
+
+	/**
+	 * Test that the expiry timestamp is set and returns the expected value.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testExpiry()
+	{
+		// Define the expected expiry date based on the resource class' $cache_duration setting.
+		$expectedExpiryDate = date('Y-m-d', time() + $this->resource->cache_duration);
+
+		// Fetch the actual expiry date set when the resource class was initialized.
+		$expiryDate = date('Y-m-d', $this->resource->last_queried + $this->resource->cache_duration);
+
+		// Confirm both dates match.
+		$this->assertEquals($expectedExpiryDate, $expiryDate);
+	}
+
+	/**
+	 * Test that the get() function performs as expected.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testGet()
+	{
+		// Confirm that no resources exist in the stored options table data.
+		$result = $this->resource->get();
+		$this->assertNotInstanceOf(\WP_Error::class, $result);
+		$this->assertIsArray($result);
+		$this->assertCount(0, $result);
+	}
+
+	/**
+	 * Test that the count() function returns the number of resources.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testCount()
+	{
+		$result = $this->resource->get();
+		$this->assertEquals($this->resource->count(), count($result));
+	}
+
+	/**
+	 * Test that the exist() function performs as expected.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testExist()
+	{
+		// Confirm that the function returns true, because no resources exist.
+		$result = $this->resource->exist();
+		$this->assertSame($result, false);
+	}
+}
diff --git a/tests/Integration/ResourceSequencesTest.php b/tests/Integration/ResourceSequencesTest.php
new file mode 100644
index 0000000..44ff76b
--- /dev/null
+++ b/tests/Integration/ResourceSequencesTest.php
@@ -0,0 +1,270 @@
+<?php
+
+namespace Tests;
+
+use lucatume\WPBrowser\TestCase\WPTestCase;
+
+/**
+ * Tests for the Integrate_ConvertKit_WPForms_Resource_Sequences class when data is present in the API.
+ *
+ * @since   1.8.9
+ */
+class ResourceSequencesTest extends \Codeception\TestCase\WPTestCase
+{
+	/**
+	 * The testing implementation.
+	 *
+	 * @var \WpunitTester
+	 */
+	protected $tester;
+
+	/**
+	 * Holds the API instance.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @var     Integrate_ConvertKit_WPForms_API
+	 */
+	private $api;
+
+	/**
+	 * Holds the ConvertKit Resource class.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @var     Integrate_ConvertKit_WPForms_Resource_Sequences
+	 */
+	private $resource;
+
+	/**
+	 * Holds the WPForms Account ID to store the Access Token and Refresh Token in WPForms's settings.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @var     string
+	 */
+	protected $wpforms_account_id = 'kit-unit-test';
+
+	/**
+	 * Performs actions before each test.
+	 *
+	 * @since   1.8.9
+	 */
+	public function setUp(): void
+	{
+		parent::setUp();
+
+		// Activate Plugin, to include the Plugin's constants in tests.
+		activate_plugins('wpforms-lite/wpforms.php');
+		activate_plugins('convertkit-wpforms/integrate-convertkit-wpforms.php');
+
+		// Include classes from /includes to test, as they won't be loaded by the Plugin
+		// because WPForms is not active.
+		require_once 'includes/class-integrate-convertkit-wpforms-api.php';
+		require_once 'includes/class-integrate-convertkit-wpforms-resource-sequences.php';
+
+		// Storing Access Token and Refresh Token in WPForms's settings.
+		wpforms_update_providers_options(
+			'convertkit',
+			array(
+				'access_token'  => $_ENV['CONVERTKIT_OAUTH_ACCESS_TOKEN'],
+				'refresh_token' => $_ENV['CONVERTKIT_OAUTH_REFRESH_TOKEN'],
+				'token_expires' => time() + 10000,
+				'label'         => 'ConvertKit WordPress',
+				'date'          => time(),
+			),
+			$this->wpforms_account_id
+		);
+
+		// Initialize the API instance.
+		$this->api = new \Integrate_ConvertKit_WPForms_API(
+			$_ENV['CONVERTKIT_OAUTH_CLIENT_ID'],
+			$_ENV['CONVERTKIT_OAUTH_REDIRECT_URI'],
+			$_ENV['CONVERTKIT_OAUTH_ACCESS_TOKEN'],
+			$_ENV['CONVERTKIT_OAUTH_REFRESH_TOKEN']
+		);
+
+		// Initialize the resource class we want to test with the API instance and WPForms Account ID.
+		$this->resource = new \Integrate_ConvertKit_WPForms_Resource_Sequences( $this->api, $this->wpforms_account_id );
+		$this->assertNotInstanceOf(\WP_Error::class, $this->resource->resources);
+
+		// Initialize the resource class, fetching resources from the API and caching them in the options table.
+		$result = $this->resource->init();
+
+		// Confirm calling init() didn't result in an error.
+		$this->assertNotInstanceOf(\WP_Error::class, $result);
+	}
+
+	/**
+	 * Performs actions after each test.
+	 *
+	 * @since   1.8.9
+	 */
+	public function tearDown(): void
+	{
+		// Disable integration, removing Access Token and Refresh Token from Plugin's settings.
+		wpforms_update_providers_options(
+			'convertkit',
+			array(
+				'access_token'  => '',
+				'refresh_token' => '',
+				'token_expires' => 0,
+				'label'         => 'ConvertKit WordPress',
+				'date'          => time(),
+			),
+			$this->wpforms_account_id
+		);
+
+		// Delete Resources from options table.
+		delete_option($this->resource->settings_name . '_' . $this->wpforms_account_id);
+		delete_option($this->resource->settings_name . '_' . $this->wpforms_account_id . '_last_queried');
+
+		// Destroy the classes we tested.
+		unset($this->api);
+		unset($this->resource);
+
+		parent::tearDown();
+	}
+
+	/**
+	 * Test that the refresh() function performs as expected.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testRefresh()
+	{
+		// Confirm that the data is stored in the options table and includes some expected keys.
+		$result = $this->resource->refresh();
+		$this->assertIsArray($result);
+		$this->assertArrayHasKey('id', reset($result));
+		$this->assertArrayHasKey('name', reset($result));
+	}
+
+	/**
+	 * Test that the expiry timestamp is set and returns the expected value.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testExpiry()
+	{
+		// Define the expected expiry date based on the resource class' $cache_duration setting.
+		$expectedExpiryDate = date('Y-m-d', time() + $this->resource->cache_duration);
+
+		// Fetch the actual expiry date set when the resource class was initialized.
+		$expiryDate = date('Y-m-d', $this->resource->last_queried + $this->resource->cache_duration);
+
+		// Confirm both dates match.
+		$this->assertEquals($expectedExpiryDate, $expiryDate);
+	}
+
+	/**
+	 * Tests that the get() function returns resources in alphabetical ascending order
+	 * by default.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testGet()
+	{
+		// Call resource class' get() function.
+		$result = $this->resource->get();
+
+		// Assert result is an array.
+		$this->assertIsArray($result);
+
+		// Assert top level array keys are preserved.
+		$this->assertArrayHasKey(array_key_first($this->resource->resources), $result);
+		$this->assertArrayHasKey(array_key_last($this->resource->resources), $result);
+
+		// Assert resource within results has expected array keys.
+		$this->assertArrayHasKey('id', reset($result));
+		$this->assertArrayHasKey('name', reset($result));
+
+		// Assert order of data is in ascending alphabetical order.
+		$this->assertEquals('Another Sequence', reset($result)[ $this->resource->order_by ]);
+		$this->assertEquals('WordPress Sequence', end($result)[ $this->resource->order_by ]);
+	}
+
+	/**
+	 * Tests that the get() function returns resources in alphabetical descending order
+	 * when a valid order_by and order properties are defined.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testGetWithValidOrderByAndOrder()
+	{
+		// Define order_by and order.
+		$this->resource->order_by = 'name';
+		$this->resource->order    = 'desc';
+
+		// Call resource class' get() function.
+		$result = $this->resource->get();
+
+		// Assert result is an array.
+		$this->assertIsArray($result);
+
+		// Assert top level array keys are preserved.
+		$this->assertArrayHasKey(array_key_first($this->resource->resources), $result);
+		$this->assertArrayHasKey(array_key_last($this->resource->resources), $result);
+
+		// Assert resource within results has expected array keys.
+		$this->assertArrayHasKey('id', reset($result));
+		$this->assertArrayHasKey('name', reset($result));
+
+		// Assert order of data is in descending alphabetical order.
+		$this->assertEquals('WordPress Sequence', reset($result)[ $this->resource->order_by ]);
+		$this->assertEquals('Another Sequence', end($result)[ $this->resource->order_by ]);
+	}
+
+	/**
+	 * Tests that the get() function returns resources in their original order
+	 * when populated with Forms and an invalid order_by value is specified.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testGetWithInvalidOrderBy()
+	{
+		// Define order_by with an invalid value (i.e. an array key that does not exist).
+		$this->resource->order_by = 'invalid_key';
+
+		// Call resource class' get() function.
+		$result = $this->resource->get();
+
+		// Assert result is an array.
+		$this->assertIsArray($result);
+
+		// Assert top level array keys are preserved.
+		$this->assertArrayHasKey(array_key_first($this->resource->resources), $result);
+		$this->assertArrayHasKey(array_key_last($this->resource->resources), $result);
+
+		// Assert resource within results has expected array keys.
+		$this->assertArrayHasKey('id', reset($result));
+		$this->assertArrayHasKey('name', reset($result));
+
+		// Assert order of data has not changed.
+		$this->assertEquals('Another Sequence', reset($result)['name']);
+		$this->assertEquals('WordPress Sequence', end($result)['name']);
+	}
+
+	/**
+	 * Test that the count() function returns the number of resources.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testCount()
+	{
+		$result = $this->resource->get();
+		$this->assertEquals($this->resource->count(), count($result));
+	}
+
+	/**
+	 * Test that the exist() function performs as expected.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testExist()
+	{
+		// Confirm that the function returns true, because resources exist.
+		$result = $this->resource->exist();
+		$this->assertSame($result, true);
+	}
+}
diff --git a/tests/Integration/ResourceTagsNoDataTest.php b/tests/Integration/ResourceTagsNoDataTest.php
new file mode 100644
index 0000000..e7e8352
--- /dev/null
+++ b/tests/Integration/ResourceTagsNoDataTest.php
@@ -0,0 +1,196 @@
+<?php
+
+namespace Tests;
+
+use lucatume\WPBrowser\TestCase\WPTestCase;
+
+/**
+ * Tests for the Integrate_ConvertKit_WPForms_Resource_Tags class when no data is present in the API.
+ *
+ * @since   1.8.9
+ */
+class ResourceTagsNoDataTest extends \Codeception\TestCase\WPTestCase
+{
+	/**
+	 * The testing implementation.
+	 *
+	 * @var \WpunitTester
+	 */
+	protected $tester;
+
+	/**
+	 * Holds the API instance.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @var     Integrate_ConvertKit_WPForms_API
+	 */
+	private $api;
+
+	/**
+	 * Holds the ConvertKit Resource class.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @var     Integrate_ConvertKit_WPForms_Resource_Tags
+	 */
+	private $resource;
+
+	/**
+	 * Holds the WPForms Account ID to store the Access Token and Refresh Token in WPForms's settings.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @var     string
+	 */
+	protected $wpforms_account_id = 'kit-unit-test';
+
+	/**
+	 * Performs actions before each test.
+	 *
+	 * @since   1.8.9
+	 */
+	public function setUp(): void
+	{
+		parent::setUp();
+
+		// Activate Plugin, to include the Plugin's constants in tests.
+		activate_plugins('wpforms-lite/wpforms.php');
+		activate_plugins('convertkit-wpforms/integrate-convertkit-wpforms.php');
+
+		// Include classes from /includes to test, as they won't be loaded by the Plugin
+		// because WPForms is not active.
+		require_once 'includes/class-integrate-convertkit-wpforms-api.php';
+		require_once 'includes/class-integrate-convertkit-wpforms-resource-tags.php';
+
+		// Storing Access Token and Refresh Token in WPForms's settings.
+		wpforms_update_providers_options(
+			'convertkit',
+			array(
+				'access_token'  => $_ENV['CONVERTKIT_OAUTH_ACCESS_TOKEN_NO_DATA'],
+				'refresh_token' => $_ENV['CONVERTKIT_OAUTH_REFRESH_TOKEN_NO_DATA'],
+				'token_expires' => time() + 10000,
+				'label'         => 'ConvertKit WordPress',
+				'date'          => time(),
+			),
+			$this->wpforms_account_id
+		);
+
+		// Initialize the API instance.
+		$this->api = new \Integrate_ConvertKit_WPForms_API(
+			$_ENV['CONVERTKIT_OAUTH_CLIENT_ID'],
+			$_ENV['CONVERTKIT_OAUTH_REDIRECT_URI'],
+			$_ENV['CONVERTKIT_OAUTH_ACCESS_TOKEN_NO_DATA'],
+			$_ENV['CONVERTKIT_OAUTH_REFRESH_TOKEN_NO_DATA']
+		);
+
+		// Initialize the resource class we want to test with the API instance and WPForms Account ID.
+		$this->resource = new \Integrate_ConvertKit_WPForms_Resource_Tags( $this->api, $this->wpforms_account_id );
+		$this->assertNotInstanceOf(\WP_Error::class, $this->resource->resources);
+
+		// Initialize the resource class, fetching resources from the API and caching them in the options table.
+		$result = $this->resource->init();
+
+		// Confirm calling init() didn't result in an error.
+		$this->assertNotInstanceOf(\WP_Error::class, $result);
+	}
+
+	/**
+	 * Performs actions after each test.
+	 *
+	 * @since   1.8.9
+	 */
+	public function tearDown(): void
+	{
+		// Disable integration, removing Access Token and Refresh Token from Plugin's settings.
+		wpforms_update_providers_options(
+			'convertkit',
+			array(
+				'access_token'  => '',
+				'refresh_token' => '',
+				'token_expires' => 0,
+				'label'         => 'ConvertKit WordPress',
+				'date'          => time(),
+			),
+			$this->wpforms_account_id
+		);
+
+		// Delete Resources from options table.
+		delete_option($this->resource->settings_name . '_' . $this->wpforms_account_id);
+		delete_option($this->resource->settings_name . '_' . $this->wpforms_account_id . '_last_queried');
+
+		// Destroy the classes we tested.
+		unset($this->api);
+		unset($this->resource);
+
+		parent::tearDown();
+	}
+
+	/**
+	 * Test that the refresh() function performs as expected.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testRefresh()
+	{
+		// Confirm that no resources exist in the stored options table data.
+		$result = $this->resource->refresh();
+		$this->assertNotInstanceOf(\WP_Error::class, $result);
+		$this->assertIsArray($result);
+		$this->assertCount(0, $result);
+	}
+
+	/**
+	 * Test that the expiry timestamp is set and returns the expected value.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testExpiry()
+	{
+		// Define the expected expiry date based on the resource class' $cache_duration setting.
+		$expectedExpiryDate = date('Y-m-d', time() + $this->resource->cache_duration);
+
+		// Fetch the actual expiry date set when the resource class was initialized.
+		$expiryDate = date('Y-m-d', $this->resource->last_queried + $this->resource->cache_duration);
+
+		// Confirm both dates match.
+		$this->assertEquals($expectedExpiryDate, $expiryDate);
+	}
+
+	/**
+	 * Test that the get() function performs as expected.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testGet()
+	{
+		// Confirm that no resources exist in the stored options table data.
+		$result = $this->resource->get();
+		$this->assertNotInstanceOf(\WP_Error::class, $result);
+		$this->assertIsArray($result);
+		$this->assertCount(0, $result);
+	}
+
+	/**
+	 * Test that the count() function returns the number of resources.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testCount()
+	{
+		$result = $this->resource->get();
+		$this->assertEquals($this->resource->count(), count($result));
+	}
+
+	/**
+	 * Test that the exist() function performs as expected.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testExist()
+	{
+		// Confirm that the function returns true, because no resources exist.
+		$result = $this->resource->exist();
+		$this->assertSame($result, false);
+	}
+}
diff --git a/tests/Integration/ResourceTagsTest.php b/tests/Integration/ResourceTagsTest.php
new file mode 100644
index 0000000..5015565
--- /dev/null
+++ b/tests/Integration/ResourceTagsTest.php
@@ -0,0 +1,270 @@
+<?php
+
+namespace Tests;
+
+use lucatume\WPBrowser\TestCase\WPTestCase;
+
+/**
+ * Tests for the Integrate_ConvertKit_WPForms_Resource_Tags class when data is present in the API.
+ *
+ * @since   1.8.9
+ */
+class ResourceTagsTest extends \Codeception\TestCase\WPTestCase
+{
+	/**
+	 * The testing implementation.
+	 *
+	 * @var \WpunitTester
+	 */
+	protected $tester;
+
+	/**
+	 * Holds the API instance.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @var     Integrate_ConvertKit_WPForms_API
+	 */
+	private $api;
+
+	/**
+	 * Holds the ConvertKit Resource class.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @var     Integrate_ConvertKit_WPForms_Resource_Tags
+	 */
+	private $resource;
+
+	/**
+	 * Holds the WPForms Account ID to store the Access Token and Refresh Token in WPForms's settings.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @var     string
+	 */
+	protected $wpforms_account_id = 'kit-unit-test';
+
+	/**
+	 * Performs actions before each test.
+	 *
+	 * @since   1.8.9
+	 */
+	public function setUp(): void
+	{
+		parent::setUp();
+
+		// Activate Plugin, to include the Plugin's constants in tests.
+		activate_plugins('wpforms-lite/wpforms.php');
+		activate_plugins('convertkit-wpforms/integrate-convertkit-wpforms.php');
+
+		// Include classes from /includes to test, as they won't be loaded by the Plugin
+		// because WPForms is not active.
+		require_once 'includes/class-integrate-convertkit-wpforms-api.php';
+		require_once 'includes/class-integrate-convertkit-wpforms-resource-tags.php';
+
+		// Storing Access Token and Refresh Token in WPForms's settings.
+		wpforms_update_providers_options(
+			'convertkit',
+			array(
+				'access_token'  => $_ENV['CONVERTKIT_OAUTH_ACCESS_TOKEN'],
+				'refresh_token' => $_ENV['CONVERTKIT_OAUTH_REFRESH_TOKEN'],
+				'token_expires' => time() + 10000,
+				'label'         => 'ConvertKit WordPress',
+				'date'          => time(),
+			),
+			$this->wpforms_account_id
+		);
+
+		// Initialize the API instance.
+		$this->api = new \Integrate_ConvertKit_WPForms_API(
+			$_ENV['CONVERTKIT_OAUTH_CLIENT_ID'],
+			$_ENV['CONVERTKIT_OAUTH_REDIRECT_URI'],
+			$_ENV['CONVERTKIT_OAUTH_ACCESS_TOKEN'],
+			$_ENV['CONVERTKIT_OAUTH_REFRESH_TOKEN']
+		);
+
+		// Initialize the resource class we want to test with the API instance and WPForms Account ID.
+		$this->resource = new \Integrate_ConvertKit_WPForms_Resource_Tags( $this->api, $this->wpforms_account_id );
+		$this->assertNotInstanceOf(\WP_Error::class, $this->resource->resources);
+
+		// Initialize the resource class, fetching resources from the API and caching them in the options table.
+		$result = $this->resource->init();
+
+		// Confirm calling init() didn't result in an error.
+		$this->assertNotInstanceOf(\WP_Error::class, $result);
+	}
+
+	/**
+	 * Performs actions after each test.
+	 *
+	 * @since   1.8.9
+	 */
+	public function tearDown(): void
+	{
+		// Disable integration, removing Access Token and Refresh Token from Plugin's settings.
+		wpforms_update_providers_options(
+			'convertkit',
+			array(
+				'access_token'  => '',
+				'refresh_token' => '',
+				'token_expires' => 0,
+				'label'         => 'ConvertKit WordPress',
+				'date'          => time(),
+			),
+			$this->wpforms_account_id
+		);
+
+		// Delete Resources from options table.
+		delete_option($this->resource->settings_name . '_' . $this->wpforms_account_id);
+		delete_option($this->resource->settings_name . '_' . $this->wpforms_account_id . '_last_queried');
+
+		// Destroy the classes we tested.
+		unset($this->api);
+		unset($this->resource);
+
+		parent::tearDown();
+	}
+
+	/**
+	 * Test that the refresh() function performs as expected.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testRefresh()
+	{
+		// Confirm that the data is stored in the options table and includes some expected keys.
+		$result = $this->resource->refresh();
+		$this->assertIsArray($result);
+		$this->assertArrayHasKey('id', reset($result));
+		$this->assertArrayHasKey('name', reset($result));
+	}
+
+	/**
+	 * Test that the expiry timestamp is set and returns the expected value.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testExpiry()
+	{
+		// Define the expected expiry date based on the resource class' $cache_duration setting.
+		$expectedExpiryDate = date('Y-m-d', time() + $this->resource->cache_duration);
+
+		// Fetch the actual expiry date set when the resource class was initialized.
+		$expiryDate = date('Y-m-d', $this->resource->last_queried + $this->resource->cache_duration);
+
+		// Confirm both dates match.
+		$this->assertEquals($expectedExpiryDate, $expiryDate);
+	}
+
+	/**
+	 * Tests that the get() function returns resources in alphabetical ascending order
+	 * by default.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testGet()
+	{
+		// Call resource class' get() function.
+		$result = $this->resource->get();
+
+		// Assert result is an array.
+		$this->assertIsArray($result);
+
+		// Assert top level array keys are preserved.
+		$this->assertArrayHasKey(array_key_first($this->resource->resources), $result);
+		$this->assertArrayHasKey(array_key_last($this->resource->resources), $result);
+
+		// Assert resource within results has expected array keys.
+		$this->assertArrayHasKey('id', reset($result));
+		$this->assertArrayHasKey('name', reset($result));
+
+		// Assert order of data is in ascending alphabetical order.
+		$this->assertEquals('gravityforms-tag-1', reset($result)[ $this->resource->order_by ]);
+		$this->assertEquals('wpforms', end($result)[ $this->resource->order_by ]);
+	}
+
+	/**
+	 * Tests that the get() function returns resources in alphabetical descending order
+	 * when a valid order_by and order properties are defined.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testGetWithValidOrderByAndOrder()
+	{
+		// Define order_by and order.
+		$this->resource->order_by = 'name';
+		$this->resource->order    = 'desc';
+
+		// Call resource class' get() function.
+		$result = $this->resource->get();
+
+		// Assert result is an array.
+		$this->assertIsArray($result);
+
+		// Assert top level array keys are preserved.
+		$this->assertArrayHasKey(array_key_first($this->resource->resources), $result);
+		$this->assertArrayHasKey(array_key_last($this->resource->resources), $result);
+
+		// Assert resource within results has expected array keys.
+		$this->assertArrayHasKey('id', reset($result));
+		$this->assertArrayHasKey('name', reset($result));
+
+		// Assert order of data is in ascending alphabetical order.
+		$this->assertEquals('wpforms', reset($result)[ $this->resource->order_by ]);
+		$this->assertEquals('gravityforms-tag-1', end($result)[ $this->resource->order_by ]);
+	}
+
+	/**
+	 * Tests that the get() function returns resources in their original order
+	 * when populated with Forms and an invalid order_by value is specified.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testGetWithInvalidOrderBy()
+	{
+		// Define order_by with an invalid value (i.e. an array key that does not exist).
+		$this->resource->order_by = 'invalid_key';
+
+		// Call resource class' get() function.
+		$result = $this->resource->get();
+
+		// Assert result is an array.
+		$this->assertIsArray($result);
+
+		// Assert top level array keys are preserved.
+		$this->assertArrayHasKey(array_key_first($this->resource->resources), $result);
+		$this->assertArrayHasKey(array_key_last($this->resource->resources), $result);
+
+		// Assert resource within results has expected array keys.
+		$this->assertArrayHasKey('id', reset($result));
+		$this->assertArrayHasKey('name', reset($result));
+
+		// Assert order of data has not changed.
+		$this->assertEquals('wpforms', reset($result)['name']);
+		$this->assertEquals('wordpress', end($result)['name']);
+	}
+
+	/**
+	 * Test that the count() function returns the number of resources.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testCount()
+	{
+		$result = $this->resource->get();
+		$this->assertEquals($this->resource->count(), count($result));
+	}
+
+	/**
+	 * Test that the exist() function performs as expected.
+	 *
+	 * @since   1.8.9
+	 */
+	public function testExist()
+	{
+		// Confirm that the function returns true, because resources exist.
+		$result = $this->resource->exist();
+		$this->assertSame($result, true);
+	}
+}
diff --git a/tests/Support/Helper/WPNotices.php b/tests/Support/Helper/WPNotices.php
new file mode 100644
index 0000000..36191ab
--- /dev/null
+++ b/tests/Support/Helper/WPNotices.php
@@ -0,0 +1,37 @@
+<?php
+namespace Tests\Support\Helper;
+
+/**
+ * Helper methods and actions related to WordPress' Admin Notices,
+ * which are then available using $I->{yourFunctionName}.
+ *
+ * @since   1.8.9
+ */
+class WPNotices extends \Codeception\Module
+{
+	/**
+	 * Confirms that an error notification is output with the given text.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @param   EndToEndTester $I              EndToEnd Tester.
+	 * @param   string         $message        Message.
+	 */
+	public function seeErrorNotice($I, $message)
+	{
+		$I->see($message, 'div.notice-error');
+	}
+
+	/**
+	 * Confirms that an error notification is not output with the given text.
+	 *
+	 * @since   1.8.9
+	 *
+	 * @param   EndToEndTester $I              EndToEnd Tester.
+	 * @param   string         $message        Message.
+	 */
+	public function dontSeeErrorNotice($I, $message)
+	{
+		$I->dontSee($message, 'div.notice-error');
+	}
+}
diff --git a/views/backend/settings-form-marketing-forms-dropdown.php b/views/backend/settings-form-marketing-forms-dropdown.php
index 5add28e..237f14d 100644
--- a/views/backend/settings-form-marketing-forms-dropdown.php
+++ b/views/backend/settings-form-marketing-forms-dropdown.php
@@ -8,6 +8,15 @@
 
 ?>
 <div class="wpforms-provider-lists wpforms-connection-block">
+<?php
+if ( ! empty( $error_message ) ) {
+	printf(
+		'<div class="wpforms-error wpforms-alert wpforms-alert-error"><p>%s</p></div>',
+		esc_html( $error_message )
+	);
+}
+?>
+
 	<h4><?php esc_html_e( 'Kit Form', 'integrate-convertkit-wpforms' ); ?></h4>
 
 	<select name="providers[<?php echo esc_attr( $this->slug ); ?>][<?php echo esc_attr( $connection_id ); ?>][list_id]" size="1">