Unity Admob Interstitial shows errors?

I found this code on Youtube and was planning to study it. Thing is, the interstitial segment shows errors. I removed the interstitial parts and the code shows no more errors. I will paste the entire thing in case it helps someone else. The link to the Youtube vid is here: Link

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using GoogleMobileAds.Api;
 using System;
 using UnityEngine.UI;
 using UnityEngine.SceneManagement;
 
 public class Admobs : MonoBehaviour
 {
     public Text adStatus;
 
     string App_ID = "XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX";
 
     string Banner_AD_ID = "ca-app-pub-3940256099942544/6300978111";
     string Interstitial_AD_ID = "ca-app-pub-3940256099942544/1033173712";
     string Video_AD_ID = "ca-app-pub-3940256099942544/5224354917";
 
 
     private BannerView bannerView;
     private InterstitialAd interstital;
     private RewardBasedVideoAd rewardBasedVideo;
 
     public string Banner_AD_ID1 { get => Banner_AD_ID2; set => Banner_AD_ID2 = value; }
     public string Banner_AD_ID2 { get => Banner_AD_ID; set => Banner_AD_ID = value; }
 
     void Start()
     {
         MobileAds.Initialize(App_ID);
     }
     private void RequestBanner()
     {
 
         // Create a 320x50 banner at the top of the screen.
         this.bannerView = new BannerView(Banner_AD_ID, AdSize.Banner, AdPosition.Bottom);
 
         // Called when an ad request has successfully loaded.
         this.bannerView.OnAdLoaded += this.HandleOnAdLoaded;
         // Called when an ad request failed to load.
         this.bannerView.OnAdFailedToLoad += this.HandleOnAdFailedToLoad;
         // Called when an ad is clicked.
         this.bannerView.OnAdOpening += this.HandleOnAdOpened;
         // Called when the user returned from the app after an ad click.
         this.bannerView.OnAdClosed += this.HandleOnAdClosed;
         // Called when the ad click caused the user to leave the application.
         this.bannerView.OnAdLeavingApplication += this.HandleOnAdLeavingApplication;
 
 
 
 
     }
 
 
 
     public void ShowBannerAD()
     {
 
         // Create an empty ad request.
         AdRequest request = new AdRequest.Builder().Build();
 
         // Load the banner with the request.
         this.bannerView.LoadAd(request);
 
     }
     public void RequestInterstitial()
     {
         // Initialize an InterstitialAd.
         this.interstitial = new InterstitialAd(Interstitial_AD_ID);
 
         // Called when an ad request has successfully loaded.
         this.interstitial.OnAdLoaded += HandleOnAdLoaded;
         // Called when an ad request failed to load.
         this.interstitial.OnAdFailedToLoad += HandleOnAdFailedToLoad;
         // Called when an ad is shown.
         this.interstitial.OnAdOpening += HandleOnAdOpened;
         // Called when the ad is closed.
         this.interstitial.OnAdClosed += HandleOnAdClosed;
         // Called when the ad click caused the user to leave the application.
         this.interstitial.OnAdLeavingApplication += HandleOnAdLeavingApplication;
 
 
         AdRequest request = new AdRequest.Builder().Build();
         this.interstital.LoadAd(request);
 
 
     }
 
 
     public void ShowInterstitialAd()
     {
 
         if (this.interstitial.IsLoaded())
         {
             this.interstitial.Show();
 
 
         }
     }
     public void RequestRewardBasedVideo()
     {
 
 
         rewardBasedVideo = RewardBasedVideoAd.Instance;
 
 
         // Create an empty ad request.
         AdRequest request = new AdRequest.Builder().Build();
         // Load the rewarded video ad with the request.
         this.rewardBasedVideo.LoadAd(request, Video_AD_ID);
 
 
     }
 
     public void ShowVideoRewardAd()
     {
         if (rewardBasedVideo.IsLoaded())
         {
             rewardBasedVideo.Show();
         }
     }
 
 
 
 
         // FOR EVENTS AND DELEGATES FOR ADS
         public void HandleOnAdLoaded(object sender, EventArgs args)
     {
         adStatus.text = "Ad Loaded";
 
 
 
         if (this.interstitial.IsLoaded())
         {
             this.interstitial.Show();
 
 
         }
 
 
 
     }
 
     public void HandleOnAdFailedToLoad(object sender, AdFailedToLoadEventArgs args)
     {
         adStatus.text = "Ad Failed To Load";
     }
 
     public void HandleOnAdOpened(object sender, EventArgs args)
     {
         MonoBehaviour.print("HandleAdOpened event received");
     }
 
     public void HandleOnAdClosed(object sender, EventArgs args)
     {
         MonoBehaviour.print("HandleAdClosed event received");
     }
 
     public void HandleOnAdLeavingApplication(object sender, EventArgs args)
     {
         MonoBehaviour.print("HandleAdLeavingApplication event received");
     }
 
 
 
 
 }