Why does my game crash on my mobile when I try to load the scene with this interstitial ad script?

The game however does not crash in unity when I press run. I added this script to the Main camera. Void GameOver() runs when the game over screen fades in. This is the script:

 using System;
 using UnityEngine;
 using GoogleMobileAds;
 using GoogleMobileAds.Api;
 
 public class interstitialAds : MonoBehaviour
 {
     private InterstitialAd interstitial;
     private bool shown;
     private int count;
 
     void Start()
     {
 
         count = PlayerPrefs.GetInt("Count");
 
         RequestInterstitial();
         if (count > 5)
         {
             GameOver();
             count = 0;
             PlayerPrefs.SetInt("Count", count);
 
         }
         count += 1;
         PlayerPrefs.SetInt("Count", count);
     }
 
     private void RequestInterstitial()
     {
 
 #if UNITY_ANDROID
         string adUnitId = "ca-app-pub-xxxxxxxxxxxxxxxxxxx";
 #elif UNITY_IPHONE
            string adUnitId = "INSERT_IOS_INTERSTITIAL_AD_UNIT_ID_HERE";
 #else
            string adUnitId = "unexpected_platform";
 #endif
 
         // Create an interstitial.
         interstitial = new InterstitialAd(adUnitId);
         AdRequest request = new AdRequest.Builder().Build();
 
         // Register for ad events.
         interstitial.AdLoaded += HandleInterstitialLoaded;
         interstitial.AdFailedToLoad += HandleInterstitialFailedToLoad;
         interstitial.AdOpened += HandleInterstitialOpened;
         interstitial.AdClosing += HandleInterstitialClosing;
         interstitial.AdClosed += HandleInterstitialClosed;
         interstitial.AdLeftApplication += HandleInterstitialLeftApplication;
         // Load an interstitial ad.
         interstitial.LoadAd(request);
     }
 
 
 
     void Update()
     {
         if (shown == false)
         {
             GameOver();
             Debug.Log("Not yet...");
         }
     }
 
 
     public void GameOver()
     {
         if (interstitial.IsLoaded())
         {
             interstitial.Show();
             shown = true;
         }
         else
         {
             Debug.Log("Interstitial is not ready yet.");
         }
     }
 
     #region Interstitial callback handlers
 
     public void HandleInterstitialLoaded(object sender, EventArgs args)
     {
         print("HandleInterstitialLoaded event received.");
     }
 
     public void HandleInterstitialFailedToLoad(object sender, AdFailedToLoadEventArgs args)
     {
         print("HandleInterstitialFailedToLoad event received with message: " + args.Message);
     }
 
     public void HandleInterstitialOpened(object sender, EventArgs args)
     {
         print("HandleInterstitialOpened event received");
     }
 
     void HandleInterstitialClosing(object sender, EventArgs args)
     {
         print("HandleInterstitialClosing event received");
     }
 
     public void HandleInterstitialClosed(object sender, EventArgs args)
     {
         print("HandleInterstitialClosed event received");
     }
 
     public void HandleInterstitialLeftApplication(object sender, EventArgs args)
     {
         print("HandleInterstitialLeftApplication event received");
     }
 
     #endregion
 }