Facebook App Invide V4.0 Notification

I upgraded my apps (iOS and Android) to the new Facebook SDK (V4.0) to use the Facebook app invite. (See http://ift.tt/1IvE4Sp).

My problem: when I send an invitation to a Facebook friend he gets a notification if he is using an Android device, but he doesn't get one if he is on iOS (even if he normally receives notifications from Facebook). Despite that, in both cases I can find the invitation in the Facebook app. So the problem is just about the notifications.

Do you know if Facebook has not implemented this part of their API or if I'm doing something wrong?

Thanks for your help.