/**
 * Fires if the received webmention is not a response but just an update notification.
 *
 * @param array $commentdata 
 */
function my_webmention_target_updated_notification_callback( array $commentdata ) {
    // Your code here.
}
add_action( 'webmention_target_updated_notification', 'my_webmention_target_updated_notification_callback' );

do_action( 'webmention_target_updated_notification', $commentdata )