Posting a score to Graph Api - Scores

Question

I am trying to use Facebook's Score Api to create a leaderboard for my iOS game but I am stuck at posting score to /USER_ID/scores.

here's my code:

NSMutableDictionary *params =  [NSMutableDictionary dictionaryWithObjectsAndKeys:
                                @"2000", @"score",
                                self.facebook.accessToken, @"access_token",
                                nil];

[self.facebook requestWithGraphPath:[NSString stringWithFormat:@"%@/scores", self.userId]
                          andParams:params 
                      andHttpMethod:@"POST" 
                        andDelegate:delegate];

however, I get this error:

Domain=facebookErrDomain Code=10000 "The operation couldn’t be completed. (facebookErrDomain error 10000.)" UserInfo=0x6ba2fd0 {error={type = mutable dict, count = 3, entries => 2 : {contents = "type"} = {contents = "OAuthException"} 3 : {contents = "message"} = {contents = "(#15) This method must be called with an app access_token."} 6 : {contents = "code"} = 15 } }

I also tried it with app access token. didn't resolve

publish_actions permission is given to the app.

It's mentioned in the document that app access token should be used but I get this error using app access token

 error =     {
    code = 102;
    message = "A user access token is required to request this resource.";
    type = OAuthException;
};

using user access token gives me this error:

error =     {
    code = 15;
    message = "(#15) This method must be called with an app access_token.";
    type = OAuthException;
};