Setting up Google Play Services

Hi,

I was wondering if anyone could help me on this problem I'm having. I've written a script to allow me to sign in to google play services and also check the leaderboards. However when I go to sign in using my internal closed build Google Play pops up, the loading sign and then nothing happens. I've done a bit of research on forums and tried using both my upload certificate and app signing key over on google cloud platform however neither work. Would anyone be able to advise if it's my code below or any other suggestions? Thanks so much!

 using UnityEngine;
 using GooglePlayGames;
 using UnityEngine.SceneManagement;
  
 public class LeaderboardsController : MonoBehaviour
 {
     public static LeaderboardsController instance;
  
     private const string LEADERBOARDS_SCORE = "CgpI5fOtyc7fEAIQaA";
  
     private void Awake()
     {
         MakeSingleton();
     }
  
  
     void Start()
     {
  
         PlayGamesPlatform.Activate();
  
  
     }
  
     private void OnEnable()
     {
  
         SceneManager.sceneLoaded += LevelWasLoaded;
     }
  
  
     private void OnDisable()
     {
         SceneManager.sceneLoaded -= LevelWasLoaded;
     }
  
  
     private void LevelWasLoaded(Scene scene, LoadSceneMode mode)
     {
         if (SceneManager.GetSceneByName(PlayerPrefsScript.GetSelectedScene()).isLoaded)
         {
  
             ReportScore(PlayerPrefsScript.GetMediumScore());
  
  
         }
  
     }
  
     void MakeSingleton()
     {
  
         if(instance == null)
         {
  
             instance = this;
             DontDestroyOnLoad(gameObject);
  
         }
  
         else
         {
             Destroy(gameObject);
         }
  
  
  
  
     }
  
     public void ConnectOrDisconnectOnGooglePlayGames()
     {
  
         if (Social.localUser.authenticated)
         {
             PlayGamesPlatform.Instance.SignOut();
  
         }
  
         else
         {
  
             Social.localUser.Authenticate((bool success) =>
             {
  
             });
  
         }
  
     }
  
  
     public void OpenLeaderboardsScore()
     {
         if (Social.localUser.authenticated)
         {
  
             PlayGamesPlatform.Instance.ShowLeaderboardUI(LEADERBOARDS_SCORE);
  
         }
  
  
  
     }
  
     void ReportScore(int score)
     {
         if (Social.localUser.authenticated)
         {
  
             Social.ReportScore(score, LEADERBOARDS_SCORE, (bool success) =>
             {
  
             });
  
         }
  
     }
  
  
 }