Sending requests explicitly stating an action and object:

FB.ui({method: 'apprequests',
   message: 'Take this bomb to blast your way to victory!',
   action_type:'send',
   object_id: 'YOUR_OBJECT_ID'  // e.g. '191181717736427'
}, function(response){

   console.log(response);
});

Action type: send
Object type: gift

Object with ID '...' cannot be retrieved.