[C#] Object not set to a reference of an Object (Google AdMob)

Having an issue with my Admob Script, the banner Ads show perfectly, however I have set up a button in the UI to test the Interstitial ads with AdMob, yet they do not show up in the game when I click the Button. The button is attached to my Canvas Element and the AdManager script is referenced to the UIHandler.

Every time I click the button in the editor, and yes I'm aware the test ads will not show if it's in the editor, I was trying to see if the button would return the correct statement or if the button would do what it's been doing which is giving me a "Object not set to a reference of an Object" error. I'm at a loss, I have no clue what's going on and I'd like to finish this before I release the next update to my game.

The full Error Code:

 NullReferenceException: Object reference not set to an instance of an object
 AdManager.OnDie () (at Assets/AdManager.cs:106)
 UnityEngine.Events.InvokableCall.Invoke () (at C:/buildslave/unity/build/Runtime/Export/UnityEvent.cs:166)
 UnityEngine.Events.UnityEvent.Invoke () (at C:/buildslave/unity/build/Runtime/Export/UnityEvent_0.cs:58)
 UnityEngine.UI.Button.Press () (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/UI/Core/Button.cs:36)
 UnityEngine.UI.Button.OnPointerClick (UnityEngine.EventSystems.PointerEventData eventData) (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/UI/Core/Button.cs:45)
 UnityEngine.EventSystems.ExecuteEvents.Execute (IPointerClickHandler handler, UnityEngine.EventSystems.BaseEventData eventData) (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/EventSystem/ExecuteEvents.cs:50)
 UnityEngine.EventSystems.ExecuteEvents.Execute[IPointerClickHandler] (UnityEngine.GameObject target, UnityEngine.EventSystems.BaseEventData eventData, UnityEngine.EventSystems.EventFunction`1 functor) (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/EventSystem/ExecuteEvents.cs:261)
 UnityEngine.EventSystems.EventSystem:Update()

Here is the Code: Note The ID's are not my ID's they are Googles test Ids

 private BannerView bannerView;
 public UIHandler UIHandle;
 public string bannerID = "ca-app-pub-3940256099942544/6300978111";
 public string interstitialID = "ca-app-pub-3940256099942544/1033173712";
 
     InterstitialAd interstitial;
 
     public void Start()
     {
         //Aquiring UIHandler
         UIHandle = GetComponent<UIHandler>();
 
 
 #if UNITY_ANDROID
         bannerID += bannerID;
 #elif UNITY_IPHONE
         string bannerID = "";
 #else
         string bannerID = "UNEXPECTED_PLATFORM";
 #endif
 
         MobileAds.Initialize(bannerID);
         MobileAds.Initialize(interstitialID);
         this.RequestBanner();
         this.RequestInterstitial();
     }
 
     private void RequestBanner()
     {
 #if UNITY_ANDROID
         bannerID += bannerID;
 #elif UNITY_IPHONE
         string bannerID = "";
 #else
         string bannerID = "UNEXPECTED_PLATFORM";
 #endif
         bannerView = new BannerView(bannerID, AdSize.SmartBanner, AdPosition.Top);
 
         //Creating an Empty Ad Request
         AdRequest newRequest = new AdRequest.Builder().AddTestDevice("").Build();
 
         //Loading Banner
         bannerView.LoadAd(newRequest);
 
         bannerView.OnAdFailedToLoad += HandleOnAdFailedToLoad;
     }
 
     //Interstitial Ads
 
     private void RequestInterstitial()
     {
 #if UNITY_ANDROID
         interstitialID += interstitialID;
 #elif UNITY_IPHONE
         string interstitialID = "";
 #else
         string interstitialID = "UNEXPECTED_PLATFORM";
 #endif
 
         //Inititialize Interstitial
         InterstitialAd interstitial = new InterstitialAd(interstitialID);
 
         // Creating an Empty Request
         AdRequest newRequest = new AdRequest.Builder().AddTestDevice("").Build();
 
         // Loading Ad
         interstitial.LoadAd(newRequest);
 
         // Ad Completed the load
         interstitial.OnAdLoaded += HandleOnAdLoaded;
 
         // Ad Failed the Load
         interstitial.OnAdFailedToLoad += HandleOnAdFailedToLoad;
 
         // Ad Closed
         interstitial.OnAdClosed += HandleOnAdClosed;
     }
 
     private void HandleOnAdClosed(object sender, EventArgs args)
     {
         MonoBehaviour.print("HandleAdClosed event received");
     }
 
     public void HandleOnAdLoaded(object sender, EventArgs args)
     {
         MonoBehaviour.print("HandleAdLoaded event received");
     }
 
     public void HandleOnAdFailedToLoad(object sender, AdFailedToLoadEventArgs args)
     {
         MonoBehaviour.print("Failed to recieve advertisement" + args.Message);
     }
 
     public void OnDie()
     {
         if (interstitial.IsLoaded())
         {
             interstitial.Show();
         }
     }