ADMob basic banner

Hey guys,
im quiet new to admobs and am struggling to put up a simple banner ad due to many tutorials, but none of them are understandale.
I just want to put up a basic banner ad to the top left of the screen but am unable to. need help.
thank you in advance…

Download:

Import:
Open your project in the Unity editor. Select Assets > Import Package > Custom Package and find the GoogleMobileAdsPlugin.unitypackage file you downloaded.

3.Add script(Assets > Create > C# Script):

using UnityEngine;
using GoogleMobileAds.Api;
public class AdManager : MonoBehaviour
    {
        public string AndroidID = "ca-app-pub-3940256099942544/6300978111";

        // Use this for initialization
        void Start()
        {
            DontDestroyOnLoad(this);
            this.RequestBanner();
        }
        
        private void RequestBanner()
        {
#if UNITY_EDITOR
            string adUnitId = "unused";
#elif UNITY_ANDROID
        string adUnitId = AndroidID;
#else
        string adUnitId = "unexpected_platform";
#endif

            // Create a banner at the top of the screen.
            BannerView bannerView = new BannerView(adUnitId, AdSize.SmartBanner, AdPosition.Top);
            // Create an empty ad request.
            AdRequest request = new AdRequest.Builder().Build();
            // Load the banner with the request.
            bannerView.LoadAd(request);
        }
    }

P.S. playing by Unity Editor will not be show the ads.

More: Banner ads  |  Unity  |  Google for Developers