Working Example

        PlayFabClientAPI.LoginWithCustomID(new LoginWithCustomIDRequest()
        {
            TitleId = PlayFabSettings.TitleId,
            CreateAccount = true,
            CustomId = SystemInfo.deviceUniqueIdentifier
        }, (loginResult) =>
        {

            PlayFabClientAPI.ExecuteCloudScript(new ExecuteCloudScriptRequest()
            {
                FunctionName = "GetUserInfoWithID",
                FunctionParameter = new Dictionary<string, string>
            {
                { "PlayerID", "11AABB1A88D63DC8" }
            }
            }, (result) =>
            {
                var account = PlayFab.SimpleJson.DeserializeObject<JsonObject>(result.FunctionResult.ToString());
                var accountJson = account["UserInfo"].ToString();
                var accountInfo = PlayFab.SimpleJson.DeserializeObject<UserAccountInfo>(accountJson, Util.ApiSerializerStrategy);

                Debug.Log("test");
                Debug.Log(accountInfo.PlayFabId);
            }, HandlePlayFabError);


        }, HandlePlayFabError);
    }