Custom route to check email notification status.

gnotice_rest_init.php

<?php 
/**
 * Custom route to check email notification status.
 *
 * @return void
 * @since  1.0
 * @author Lax Mariappan <lax@webdevstudios.com>
 */
function gnotice_rest_init() {

	$namespace = 'api-gnotice/v1';
	$route     = 'check-email-response';

	register_rest_route(
		$namespace,
		$route,
		array(
			'methods'             => \WP_REST_Server::READABLE,
			'callback'            => 'get_email_notification',
			'permission_callback' => 'permission_callback' => function() { return current_user_can('edit_posts'); },
		)
	);
}

add_action( 'rest_api_init', 'gnotice_rest_init' );