Rewarded ad only works once

hey, code below shows rewarded ad code and its reward, this code works perfectly fine but after first reward, button doesn't work anymore, it doesn't do anything, can you guys help? thanks

 using UnityEngine;
 using UnityEngine.UI;
 using UnityEngine.Advertisements;
 using UnityEngine.SceneManagement;
  
 public class RewardedAdsButton : MonoBehaviour, IUnityAdsLoadListener, IUnityAdsShowListener
 {
     [SerializeField] Button _showAdButton;
     [SerializeField] string _androidAdUnitId = "Rewarded_Android";
     [SerializeField] string _iOSAdUnitId = "Rewarded_iOS";
     string _adUnitId = null; // This will remain null for unsupported platforms
  
     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;
     }
  
     // Load content to the Ad Unit:
     public void LoadAd()
     {
         // IMPORTANT! Only load content AFTER initialization (in this example, initialization is handled in a different script).
         Debug.Log("Loading Ad: " + _adUnitId);
         Advertisement.Load(_adUnitId, this);
     }
  
     // If the ad successfully loads, add a listener to the button and enable it:
     public void OnUnityAdsAdLoaded(string adUnitId)
     {
         Debug.Log("Ad Loaded: " + 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;
         }
     }
  
     // Implement a method to execute when the user clicks the button:
     public void ShowAd()
     {
         // Disable the button:
         _showAdButton.interactable = false;
         // Then show the ad:
         Advertisement.Show(_adUnitId, this);
     }
  
     // Implement the Show Listener's OnUnityAdsShowComplete callback method to determine if the user gets a reward:
     public void OnUnityAdsShowComplete(string adUnitId, UnityAdsShowCompletionState showCompletionState)
     {
         if (adUnitId.Equals(_adUnitId) && showCompletionState.Equals(UnityAdsShowCompletionState.COMPLETED))
         {
             Debug.Log("Unity Ads Rewarded Ad Completed");
             // Grant a reward.
            
                 SceneManager.LoadScene(SceneManager.GetActiveScene().buildIndex);
                 Debug.Log("Hey IM lOaDEd");
            
             // Load another ad:
             Advertisement.Load(_adUnitId, this);
         }
     }
  
     // 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();
     }
 }