How to redirect through a notification?

I'm sending notifications to registered users through Facebook about new events. How do I redirect the user to the event URL sent through the Facebook API?

private function sendNotification($userFbId, $message, $url){
    $attachment = array(
      'access_token' => Configure::read('fb_id').'|'.Configure::read('fb_secret'),
      'href' => $url, 
      'template' => $message,
    );
    try {
        $api = $this->Facebook->api('/'.$userFbId.'/notifications/', 'POST',  $attachment);
    } catch (Exception $e) {
        $api = $e->getMessage();
    }
    return $api;
}