Google Admob help

Admob ad all is correct but have error

where am I making all the wrong codes?

no error but ad

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using GoogleMobileAds.Api;

public class admobreklam : MonoBehaviour
{
public string AppID;
public string BannerAdUnityID;

private BannerView bannerView;

void Start()
{
MobileAds.Initialize(AppID);

bannerView = new BannerView(BannerAdUnityID, AdSize.Banner, AdPosition.Top);
bannerView.LoadAd(new AdRequest.Builder().Build());

}


}


and

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using System;
using GoogleMobileAds.Api;
using UnityEngine.SceneManagement;

public class admobinterstital : MonoBehaviour
{

public string AppID;
public string InterstitialAdUnityID;

private InterstitialAd interstitialAd;

public string levelToLoad;

void Start()
{
MobileAds.Initialize(AppID);

interstitialAd = new InterstitialAd(InterstitialAdUnityID);
interstitialAd.LoadAd(new AdRequest.Builder().Build());

interstitialAd.OnAdClosed += HandlerOnClosed;

}
public void HandlerOnClosed (object sender, EventArgs args)
{
SceneManager.LoadSceneAsync(levelToLoad);
}

public void ShowAd(string level)
{
if (interstitialAd.IsLoaded())
{
interstitialAd.Show();
} else
{
SceneManager.LoadSceneAsync(levelToLoad);
}
levelToLoad = level;
}

}