Send Facebook Notification as html format

Question

I am using facebook toolkit v.3 and I am trying to send notifications in html format. How could this be? Am I missing something?

this is the call

var _connectSession = new ConnectSession(Properties.FacebookKey, Properties.FacebookSecret);
Api _facebookAPI = new Api(_connectSession);
_facebookAPI.Notifications.SendEmail(fbUID, "Title", "Html Message", null);

Thanks