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 : 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();
             }
         }
     }