I created a game for iPad and I want to challenge my facebook friends.

I follow the iOS tutorial in "facebook dev docs", with the "Smash game", but it doesn't explain how to challenge a friend directly to a game.

I will explain with an example:

I want to start a new match and I want challenge a friend on facebook. Then I send him a request to install the app and when I detect that its app is installed I send him a request to play vs me.

Then, when I finish the match I sent him my result and my friend do the same thing. But if I and my friend don't finish the match it is not possible to send another challenge.

This scenario is not explained by facebook sdk. Is it necessary to use another instrument to do this situation?