Game crashes after unity ad finished?

I fixed it. Few things someone should check if he has problem with ads. I am using ads 4.1.0 at the moment of writing.

1. There is problem with listeners so you have 2 solutions:

• Remove listeners completely and use button on click

• Keep listeners but add bool showAd as I did in code below.

  ---

2. OnUnityAdsShowComplete should give award in Coroutine. This was the reason why game crashed.

Code after fixing:

 using System.Collections;
 using UnityEngine;
 using UnityEngine.Advertisements;
 using UnityEngine.UI;
 
 public class RewardedAdsButton : MonoBehaviour, IUnityAdsLoadListener, IUnityAdsShowListener
 {
     [SerializeField] Button _showAdButton;
 #if UNITY_ANDROID
     [SerializeField] string _androidAdUnitId = "Rewarded_Android";
 #elif UNITY_IOS
     [SerializeField] string _iOSAdUnitId = "Rewarded_iOS";
 #endif
     public BuildingShutdownPanelScript buildingShutdownPanelScript;
     string _adUnitId = null; // This will remain null for unsupported platforms
     private static bool showAd = false;
     void Awake()
     {
         // Get the Ad Unit ID for the current platform:
 #if UNITY_IOS
         _adUnitId = _iOSAdUnitId;
 #elif UNITY_ANDROID
         _adUnitId = _androidAdUnitId;
 #endif
 
         //Disable the button until the ad is ready to show:
         _showAdButton.interactable = false;
     }
     public void OnEnable()
     {
         if (Advertisement.isInitialized && _showAdButton.interactable != true)
         {
             LoadAd();
         }
     }
     // Load content to the Ad Unit:
     public void LoadAd()
     {
 #if UNITY_IOS
         _adUnitId = _iOSAdUnitId;
 #elif UNITY_ANDROID
         _adUnitId = _androidAdUnitId;
 #endif
         // IMPORTANT! Only load content AFTER initialization (in this example, initialization is handled in a different script).
 
         Advertisement.Load(_adUnitId, this);
     }
 
     // If the ad successfully loads, add a listener to the button and enable it:
     public void OnUnityAdsAdLoaded(string adUnitId)
     {
 
         if (adUnitId.Equals(_adUnitId))
         {
             // Configure the button to call the ShowAd() method when clicked:
             _showAdButton.onClick.AddListener(ShowAd);
             // Enable the button for users to click:
             _showAdButton.interactable = true;
             showAd = false;
         }
     }
 
     // Implement a method to execute when the user clicks the button:
     public void ShowAd()
     {
         if (!showAd)
         {
             // Disable the button:
             _showAdButton.interactable = false;
             // Then show the ad:
             Advertisement.Show(_adUnitId, this);
             showAd = true;
         }
     }
 
     // Implement the Show Listener's OnUnityAdsShowComplete callback method to determine if the user gets a reward:
     public void OnUnityAdsShowComplete(string adUnitId, UnityAdsShowCompletionState showCompletionState)
     {
         if (showAd)
         {
             if (adUnitId.Equals(_adUnitId) && showCompletionState.Equals(UnityAdsShowCompletionState.COMPLETED))
             {
                 // Grant a reward.
                 StartCoroutine(reward());
                 // Load another ad:
                 _showAdButton.onClick.RemoveListener(ShowAd);
                 Advertisement.Load(_adUnitId, this);
 
             }
         }
 
     }
     private IEnumerator reward()
     {
         yield return null;
         buildingShutdownPanelScript.WatchAd();
     }
     // Implement Load and Show Listener error callbacks:
     public void OnUnityAdsFailedToLoad(string adUnitId, UnityAdsLoadError error, string message)
     {
         Debug.Log($"Error loading Ad Unit {adUnitId}: {error.ToString()} - {message}");
         // Use the error details to determine whether to try to load another ad.
     }
 
     public void OnUnityAdsShowFailure(string adUnitId, UnityAdsShowError error, string message)
     {
         Debug.Log($"Error showing Ad Unit {adUnitId}: {error.ToString()} - {message}");
         // Use the error details to determine whether to try to load another ad.
     }
 
     public void OnUnityAdsShowStart(string adUnitId) { }
     public void OnUnityAdsShowClick(string adUnitId) { }
 
     void OnDestroy()
     {
         // Clean up the button listeners:
         _showAdButton.onClick.RemoveAllListeners();
     }
 }

Hope you find this helpful!