Integrate unity ads error at the second play

Question

I added Unity Ads to my project. At the first run at all works good and it show that an ad will show, but when I hit play the second time it give me this error

MissingReferenceException: The object of type 'GameObject' has been destroyed but you are still trying to access it. Your script should either check if it is null or you should not destroy the object.

This is my script for the ads :

public class Monetization : MonoBehaviour, IUnityAdsListener
{
    string GooglePlay_ID = "****";
    bool GameMode = true;
   
    string myPlacementId = "rewardedVideo";

    void Start()
    {
        Advertisement.AddListener(this);
        Advertisement.Initialize(GooglePlay_ID, GameMode);
       
    } 

    public void ShowRewardedVideo()
    {
        // Check if UnityAds ready before calling Show method:
        if (Advertisement.IsReady(myPlacementId))
        {
            Advertisement.Show(myPlacementId);
        }
        else
        {
            Debug.Log("Rewarded video is not ready at the moment! Please try again later!");
        }
    }

    // Implement IUnityAdsListener interface methods:
    public void OnUnityAdsDidFinish(string placementId, ShowResult showResult)
    {
        // Define conditional logic for each ad completion status:
        if (showResult == ShowResult.Finished)
        {
            // Reward the user for watching the ad to completion.

           
            SceneManager.LoadScene(4);
        }
       
        else if (showResult == ShowResult.Skipped)
        {
            // Do not reward the user for skipping the ad.
        }
        else if (showResult == ShowResult.Failed)
        {
            Debug.LogWarning("The ad did not finish due to an error.");
        }
    }

    public void OnUnityAdsReady(string placementId)
    {
        // If the ready Placement is rewarded, show the ad:
        if (placementId == myPlacementId)
        {
            // Optional actions to take when the placement becomes ready(For example, enable the rewarded ads button)
        }
    }

    public void OnUnityAdsDidError(string message)
    {
        // Log the error.
    }

    public void OnUnityAdsDidStart(string placementId)
    {
        // Optional actions to take when the end-users triggers an ad.
    }
}

Answer 1

When you load a new scene, the game objects in the previous scene will be destroyed. To prevent this add the following function in your Monetization script.

void Awake() {
DontDestroyOnLoad(this.gameObject);
}