Unity leaderboard on mac os x device - Pubnub, Playfab or Firebase?

I am currently making a a leaderboard feature for my Mac OS X Unity game. I first tried Playfab but I kept getting an error saying "PlayFabException: Must be logged in to call this method PlayFab". I can't find a way to resolve this.

I have 2 scripts that does this, this is the code for the PlayFabManger script:

`using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using PlayFab;
using PlayFab.ClientModels;
using System;

    public class PlayFabManager : MonoBehaviour

    //public static PlayFabManager instance;
    // Start is called before the first frame update
    void Start()
    {
        //instance = this;
        if (string.IsNullOrEmpty(PlayFabSettings.staticSettings.TitleId))
        {
            /*
            Please change the titleId below to your own titleId from PlayFab Game Manager.
            If you have already set the value in the Editor Extensions, this can be skipped.
            */
            PlayFabSettings.staticSettings.TitleId = "F9F3D";
        }
        Login();
    }

    // Update is called once per frame
    void Update()
    {

    }

    void Login()
    {
        var request = new LoginWithCustomIDRequest
        {
            CustomId = SystemInfo.deviceUniqueIdentifier,
            CreateAccount = true
        };
        PlayFabClientAPI.LoginWithCustomID(request, OnSuccess, OnError);
    }

    //private void OnLoginSuccess(LoginResult result)
    //{
    //    //>> Call Client API here <<
    //    var getStoreItemsRequest = new GetStoreItemsRequest { StoreId = "[YourStoreId]" };// Please change this value to your own storeId from PlayFab Game Manager
    //    PlayFabClientAPI.GetStoreItems(getStoreItemsRequest, OnGetSuccess, OnError);

    //}


    void OnSuccess(LoginResult result)
    {
        print("Successful login create");
    }

    public void SendLeaderBoard(int score)
    {
        var request = new UpdatePlayerStatisticsRequest
        {
            Statistics = new List<StatisticUpdate>
            {
                new StatisticUpdate
                {
                    StatisticName = "PlatformScore",
                    Value = score
                }
            }
        };
        PlayFabClientAPI.UpdatePlayerStatistics(request, OnLeaderboardUpdate, OnError);
    }

    void OnLeaderboardUpdate(UpdatePlayerStatisticsResult result)
    {
        print("Successful leaderboard sent");
    }

    void OnError(PlayFabError error)
    {
        print("Error while logging in/creating account!");
        print(error.GenerateErrorReport());
    }

    public void GetLeaderBoard()
    {
        var request = new GetLeaderboardRequest
        {
            StatisticName = "PlatformScore",
            StartPosition = 0,
            MaxResultsCount = 10
        };
        PlayFabClientAPI.GetLeaderboard(request, OnLeaderboardGet, OnError);
    }

    private void OnLeaderboardGet(GetLeaderboardResult result)
    {
        foreach (var item in result.Leaderboard)
        {
            print(item.Position + " " + item.PlayFabId + " " + item.StatValue);
        }
    }

    }

`

I also have a line of code in another script that is called at the start method and refers to the above script, where I pass in a Playerprefs.GetInt variable: playFabManager.SendLeaderBoard(PlayerPrefs.GetInt("TtlPoints"));

Does anyone have any idea on resolving this error? Is there an easier way to achieve this leaderboard feature on Mac OS X using other extensions such as firebase or pubnub?

Sorry for my English, looking forward to hearing from you.

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