Facebook SDK for Unity: check if an invite has been sent and give award to the player

I’m using this script to check if the player has sent an invitation to his friends and then give him a reward.

the script is commented .

this is what I get as a result : 87061-screenshot-2017-01-31-16-34-02.png
it means that there is something wrong with this line IEnumerable invitesSent = (IEnumerable)responseObject[“to”];
please read the script it is commented

I’m running on android
public void ChalengeFriends ()
{
FB.AppRequest (
“Here is a free gift!”,
null,
new List (){ “app_users” },
null, null, “data”, “Challenge your friends!”,
ChalengeFriendsCallBack1
);
}

	void ChalengeFriendsCallBack1 (IAppRequestResult result)
	{
		if (result.Cancelled) {
		} else if (!string.IsNullOrEmpty (result.Error)) {
		} else {
			text5.text = " challenge success : " + result.RawResult;
			text5.text = "1===  "+text5.text;
			
			/* //method 1 : not working
			IDictionary<string,object> data = result.ResultDictionary;
			text5.text = "2===  "+text5.text;
			List<object> friends = (List<object>)data ["to"];  //something wrong here
			text5.text = "3";
			text5.text = "" + friends.Count;
			if (friends.Count == 2) {
                // Give user a free item
				text5.text = "reward success------" + friends.Count;
				//.........
			}*/
			
			// method 2 : not working
			var responseObject = Json.Deserialize(result.RawResult) as Dictionary<string, object>;
			text5.text = "3===  "+text5.text;  // the execution stops at this line 
			IEnumerable<object> invitesSent = (IEnumerable<object>)responseObject["to"];
           // List<string> objectArray = (List<string>)responseObject["to"]; //not working
			text5.text = "4===  "+text5.text;

            if (objectArray.Count() == 1)
            {
                // Give user a free item
				text5.text = "reward yeeeeeeeeeeeees------" +objectArray.Count();
            }
		}
	}

If anyone is still searching here is an example in comments: