Problem implementing Leaderboard button

Hello. I want to add a leaderboard to my android game. I've created one in google play console successfully. I've used three scripts for managing score, leaderbooards and game/player:

1. LeaderBoardManagerScript where I manage everything related to leaderboards (login, add score and show leaderboard.

2. ScoreScript, where I manage everything related to score system

3. Player script, where I manage player and game behavior.

    using System.Collections;
    using System.Collections.Generic;
    using UnityEngine;
    using GooglePlayGames;
    using UnityEngine.SocialPlatforms;
    using UnityEngine.UI;
    
    public class LeaderboardManagerScript : MonoBehaviour
    {
        public int score;
        public static LeaderboardManagerScript current;
        
        private void Awake()
        {
            if (current == null)
                current = this;
        }
    
        // Start is called before the first frame update
        void Start()
        {
            PlayGamesPlatform.Activate();
            Login();
        }
    
        // Update is called once per frame
        void Update()
        { 
            
        }
    
        public void Login()
        {
            Social.localUser.Authenticate((bool success) => 
            { 
            });
        }
    
        public void AddScore()
        {
            Social.ReportScore(ScoreScript.current.score, Leaderboard.leaderboard_best_scores, (bool success) =>
            {
            });
        }
    
        public void ShowLeaderboard()
        {
            if (Social.localUser.authenticated)
            {
                PlayGamesPlatform.Instance.ShowLeaderboardUI(Leaderboard.leaderboard_best_scores);
            }
            else
            {
                Login();
            }
        }
    }
    
   
    using System.Collections;
    using System.Collections.Generic;
    using UnityEngine;
    using UnityEngine.UI;
    
    public class ScoreScript : MonoBehaviour
    {
        public int score;
        public Text scoreText;
        public Text highScoreText;
    
        public static ScoreScript current;
    
        private void Awake()
        {
            if (current == null)
                current = this;
        }
    
        void Start()
        {
            score = 0;
        }
    
        void Update()
        {
            scoreText.text = score.ToString();
        }
    
        private void OnTriggerEnter(Collider other)
        {
            if (other.gameObject.tag == "Score")
            {
                score++;
                    PlayerScript.current.playerSpeed = PlayerScript.current.playerSpeed + 3;
            }
                
    
            if (other.gameObject.tag == "Score2")
            {
                score += 2;
                    PlayerScript.current.playerSpeed = PlayerScript.current.playerSpeed + 3;
            }
    
            if (other.gameObject.tag == "Jackpot") 
            { 
                score += 5;
                    PlayerScript.current.playerSpeed = PlayerScript.current.playerSpeed + 5;
            }
        }  
    
        public void CheckHighScore()
        {
            if (PlayerPrefs.HasKey("highScore"))
            {
                if (score > PlayerPrefs.GetInt("highScore"))
                    PlayerPrefs.SetInt("highScore", score); 
            }
            else
                PlayerPrefs.SetInt("highScore", score); 
    
            highScoreText.text = PlayerPrefs.GetInt("highScore").ToString(); 
        }
    }
   
   

I've created a button in canvas for leaderboard, set the onclick event to playerScript where I put the following void

     public void ShowLeaderboard()
     {
         LeaderboardManagerScript.current.ShowLeaderboard();
     }

when I run the game, if I push the Leaderboard button, I get a null reference exception. Not sure why, so I'm asking help...