Send error response to REST endpoint

get_email_notification.php

<?php 
/**
 * Send error response to REST endpoint.
 *
 * @return Error object
 * @since  1.0
 * @author Lax Mariappan <lax@webdevstudios.com>
 */
function get_email_notification() {
	if ( isset( $_GET['id'] ) ) {
		$id = sanitize_text_field(
			wp_unslash( $_GET['id'] )
		);

		$error = get_post_meta( $id, 'email_notification', true );

		if ( $error ) {
			$data = json_decode( $error );
			return new \WP_REST_Response(
				array(
					'code'    => $data->code,
					'message' => wp_unslash( $data->message ),
				)
			);
		}
	}

}