diff --git a/admin/class-convertkit-admin-tinymce.php b/admin/class-convertkit-admin-tinymce.php
index 2be0e35d8..178f83f11 100644
--- a/admin/class-convertkit-admin-tinymce.php
+++ b/admin/class-convertkit-admin-tinymce.php
@@ -21,7 +21,7 @@ class ConvertKit_Admin_TinyMCE {
 	public function __construct() {
 
 		// Outputs the TinyMCE and QuickTag Modal.
-		add_action( 'wp_ajax_convertkit_admin_tinymce_output_modal', array( $this, 'output_modal' ) );
+		add_action( 'rest_api_init', array( $this, 'register_routes' ) );
 
 		// Add filters to register QuickTag Plugins.
 		add_action( 'admin_enqueue_scripts', array( $this, 'register_quicktags' ) ); // WordPress Admin.
@@ -34,29 +34,57 @@ public function __construct() {
 
 	}
 
+	/**
+	 * Register REST API routes.
+	 *
+	 * @since   3.1.8
+	 */
+	public function register_routes() {
+
+		// Register route to return all blocks registered by the Plugin.
+		register_rest_route(
+			'kit/v1',
+			'/tinymce/output-modal',
+			array(
+				'methods'             => WP_REST_Server::CREATABLE,
+				'args'                => array(
+					'shortcode'   => array(
+						'required'          => true,
+						'sanitize_callback' => 'sanitize_text_field',
+					),
+					'editor_type' => array(
+						'required'          => true,
+						'sanitize_callback' => 'sanitize_text_field',
+					),
+				),
+				'callback'            => function ( $request ) {
+					ob_start();
+					$this->output_modal( $request['shortcode'], $request['editor_type'] );
+					return ob_get_clean();
+				},
+
+				// Only refresh resources for users who can edit posts.
+				'permission_callback' => function () {
+					return current_user_can( 'edit_posts' );
+				},
+			)
+		);
+
+	}
+
 	/**
 	 * Loads the view for a shortcode's modal in the TinyMCE and Text Editors.
 	 *
 	 * @since   1.9.6
+	 *
+	 * @param   string $shortcode_name Shortcode Name.
+	 * @param   string $editor_type    Editor Type (tinymce|quicktags).
 	 */
-	public function output_modal() {
-
-		// Check nonce.
-		check_ajax_referer( 'convertkit_admin_tinymce', 'nonce' );
+	public function output_modal( $shortcode_name, $editor_type ) { // phpcs:ignore Generic.CodeAnalysis.UnusedFunctionParameter.FoundAfterLastUsed
 
 		// Get shortcodes.
 		$shortcodes = convertkit_get_shortcodes();
 
-		// Bail if no shortcode or editor type is specified.
-		if ( ! isset( $_REQUEST['shortcode'] ) || ! isset( $_REQUEST['editor_type'] ) ) {
-			require_once CONVERTKIT_PLUGIN_PATH . '/views/backend/tinymce/modal-missing.php';
-			die();
-		}
-
-		// Get requested shortcode name.
-		$shortcode_name = sanitize_text_field( wp_unslash( $_REQUEST['shortcode'] ) );
-		$editor_type    = sanitize_text_field( wp_unslash( $_REQUEST['editor_type'] ) );
-
 		// If the shortcode is not registered, return a view in the modal to tell the user.
 		if ( ! isset( $shortcodes[ $shortcode_name ] ) ) {
 			require_once CONVERTKIT_PLUGIN_PATH . '/views/backend/tinymce/modal-missing.php';
@@ -118,7 +146,8 @@ public function register_quicktags() {
 			'convertkit-admin-quicktags',
 			'convertkit_admin_tinymce',
 			array(
-				'nonce' => wp_create_nonce( 'convertkit_admin_tinymce' ),
+				'ajaxurl' => rest_url( 'kit/v1/tinymce/output-modal' ),
+				'nonce'   => wp_create_nonce( 'wp_rest' ),
 			)
 		);
 
@@ -160,7 +189,8 @@ public function register_tinymce_plugins( $plugins ) {
 			'convertkit-admin-editor',
 			'convertkit_admin_tinymce',
 			array(
-				'nonce' => wp_create_nonce( 'convertkit_admin_tinymce' ),
+				'ajaxurl' => rest_url( 'kit/v1/tinymce/output-modal' ),
+				'nonce'   => wp_create_nonce( 'wp_rest' ),
 			)
 		);
 
diff --git a/includes/class-wp-convertkit.php b/includes/class-wp-convertkit.php
index ecafc5792..3dbb8f8b6 100644
--- a/includes/class-wp-convertkit.php
+++ b/includes/class-wp-convertkit.php
@@ -96,7 +96,6 @@ private function initialize_admin() {
 		$this->classes['admin_setup_wizard_landing_page']     = new ConvertKit_Admin_Setup_Wizard_Landing_Page();
 		$this->classes['admin_setup_wizard_plugin']           = new ConvertKit_Admin_Setup_Wizard_Plugin();
 		$this->classes['admin_setup_wizard_restrict_content'] = new ConvertKit_Admin_Setup_Wizard_Restrict_Content();
-		$this->classes['admin_tinymce']                       = new ConvertKit_Admin_TinyMCE();
 
 		/**
 		 * Initialize integration classes for the WordPress Administration interface.
@@ -183,6 +182,7 @@ private function initialize_frontend() {
 	private function initialize_global() {
 
 		$this->classes['admin_notices']                               = new ConvertKit_Admin_Notices();
+		$this->classes['admin_tinymce']                               = new ConvertKit_Admin_TinyMCE();
 		$this->classes['admin_refresh_resources']                     = new ConvertKit_Admin_Refresh_Resources();
 		$this->classes['blocks_convertkit_broadcasts']                = new ConvertKit_Block_Broadcasts();
 		$this->classes['blocks_convertkit_content']                   = new ConvertKit_Block_Content();
diff --git a/resources/backend/js/editor.js b/resources/backend/js/editor.js
index 0d9fa9e46..eae530805 100644
--- a/resources/backend/js/editor.js
+++ b/resources/backend/js/editor.js
@@ -55,14 +55,13 @@ function convertKitTinyMCERegisterPlugin(block) {
 				});
 
 				// Perform an AJAX call to load the modal's view.
-				fetch(ajaxurl, {
+				fetch(convertkit_admin_tinymce.ajaxurl, {
 					method: 'POST',
 					headers: {
 						'Content-Type': 'application/x-www-form-urlencoded',
+						'X-WP-Nonce': convertkit_admin_tinymce.nonce,
 					},
 					body: new URLSearchParams({
-						action: 'convertkit_admin_tinymce_output_modal',
-						nonce: convertkit_admin_tinymce.nonce,
 						editor_type: 'tinymce',
 						shortcode: block.name,
 					}),
diff --git a/resources/backend/js/quicktags.js b/resources/backend/js/quicktags.js
index 921fb45fa..2bf45c5d2 100644
--- a/resources/backend/js/quicktags.js
+++ b/resources/backend/js/quicktags.js
@@ -21,14 +21,13 @@ for (const block in convertkit_quicktags) {
 function convertKitQuickTagRegister(block) {
 	QTags.addButton('convertkit-' + block.name, block.title, function () {
 		// Perform an AJAX call to load the modal's view.
-		fetch(ajaxurl, {
+		fetch(convertkit_admin_tinymce.ajaxurl, {
 			method: 'POST',
 			headers: {
 				'Content-Type': 'application/x-www-form-urlencoded',
+				'X-WP-Nonce': convertkit_admin_tinymce.nonce,
 			},
 			body: new URLSearchParams({
-				action: 'convertkit_admin_tinymce_output_modal',
-				nonce: convertkit_admin_tinymce.nonce,
 				editor_type: 'quicktags',
 				shortcode: block.name,
 			}),