fix: store subscriber data (#496)

Store the subscriber data while the user submits the form on the Maintenance Mode page.

Author: girishpanchal30

includes/classes/wp-maintenance-mode.php

@@ -1388,7 +1388,7 @@ public function send_contact() {
 		 */
 		public function otter_add_subscriber( $form_data ) {
 			if ( $form_data ) {
-				$input_data = $form_data->get_payload_field( 'formInputsData' );
+				$input_data = $form_data->get_data_from_payload( 'formInputsData' );
 				$input_data = array_map(
 					function( $input_field ) {
 						if ( isset( $input_field['type'] ) && 'email' === $input_field['type'] ) {