Unity and PlayFab Leaderboard

Question

I seem to be struggling with the below script. It keeps telling me Object reference not set to an instance of an object LoseScene.Start () (at Assets/Scripts/LoseScene.cs:17)

public class LoseScene : MonoBehaviour
{
    public PlayfabManager playfabManager;
    
    [SerializeField] private TMP_Text _scoreText;

    private void Start()
    {
        var score = PlayerPrefs.GetInt("score");
        _scoreText.text = score.ToString();
        playfabManager.SendLeaderboard(score);
    }

    public void RestartGame()
    {
        SceneManager.LoadScene(1);
    }

    public void QuitToMenu()
    {
        SceneManager.LoadScene(0);
    }
}