GetTopNRankersFromFacebook does not return friends' scores

Question

I have setup several Test users via Facebook developer account. They are friends of each other. When I tried to get friends' scores using

GetTopNRankersFromFacebook

. It only returns the user himself.

I have used 

user_friends

 permission and linked user facebook account. Anything did I miss?

 

    public void FbLogin()
    {
        var perms = new List<string>() { "public_profile", "email", "user_friends" };
        FB.LogInWithReadPermissions(perms, AuthCallback);
    }

    private void AuthCallback(ILoginResult result)
    {
        if (FB.IsLoggedIn)
        {
            // AccessToken class will have session details
            var aToken = Facebook.Unity.AccessToken.CurrentAccessToken;

            App42API.Initialize(ConstVariables.APP42_API_KEY, ConstVariables.APP42_SECRET_KEY);
            SocialService socialService = App42API.BuildSocialService();

            socialService.LinkUserFacebookAccount(aToken.UserId, aToken.TokenString, new LinkCallBack());
            scoreBoardService = new ScoreBoardService(ConstVariables.APP42_API_KEY, ConstVariables.APP42_SECRET_KEY);
        }
        else
        {
            Debug.Log("User cancelled login");
        }
    }

Result:

Success Value : {"app42":{"response":{"success":true,"games":{"game":{"name":"Speedy Words","scores":{"score":{"userName":"100407165057496","value":2,"createdOn":"2020-10-26T13:52:03.000Z","scoreId":"_v3sHFvO2uPFR+vv8Jqn06zwgFScw=","facebookProfile":{"name":"Open Graph Test User","id":"100407165057496","picture":"https://platform-lookaside.fbsbx.com/platform/profilepic/?asid=100407165057496&height=50&width=50&ext=1606317087&hash=AeR07F78LainEVBPhHs"}}}}}}}}