Error when trying to implement admob

I have an issue that I have tried fixing for a fex hours now, I tried implementing Google Admob to my game, here's my code :

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using GoogleMobileAds.Api;
 using GoogleMobileAds;
 
 public class AdScript : MonoBehaviour
 {
     
     private BannerView bannerView;
 
     void Start()
     {
         string appID = "ca-app-pub-8918029046269211~6739827694";
 
         MobileAds.Initialize(appID);
 
         RequestBanner();
         DisplayBanner();
     }
 
     private void RequestBanner()
     {
         string adBannerID = "ca-app-pub-3940256099942544/6300978111";
         bannerView = new BannerView(adBannerID, AdSize.SmartBanner, AdPosition.Bottom);
         AdRequest adRequest = new AdRequest.Builder().AddTestDevice("2077ef9a63d2b398840261c8221a0c9b").Build();
         bannerView.LoadAd(adRequest);
     }
 
     private void DisplayBanner()
     {
         bannerView.Show();
     }
 }
 

Bur I get this error :

 Stopped polling job due to exception: System.NullReferenceException: Object reference not set to an instance of an object
   at GooglePlayServices.UnityCompat.VersionFromAndroidSDKVersionsEnum (System.String enumName, System.String fallbackPrefKey, System.Int32 fallbackValue) [0x00000] in /Users/smiles/dev/src/unity-jar-resolver/source/PlayServicesResolver/src/UnityCompat.cs:66 
   at GooglePlayServices.UnityCompat.GetAndroidTargetSDKVersion () [0x00015] in /Users/smiles/dev/src/unity-jar-resolver/source/PlayServicesResolver/src/UnityCompat.cs:115 
   at GooglePlayServices.PlayServicesResolver.CanEnableJetifierOrPromptUser (System.String titlePrefix) [0x000ae] in /Users/smiles/dev/src/unity-jar-resolver/source/PlayServicesResolver/src/PlayServicesResolver.cs:2236 
   at GooglePlayServices.PlayServicesResolver.ResolveUnsafe (System.Action`1[T] resolutionComplete, System.Boolean forceResolution, System.Boolean isAutoResolveJob, System.Boolean closeWindowOnCompletion) [0x00012] in /Users/smiles/dev/src/unity-jar-resolver/source/PlayServicesResolver/src/PlayServicesResolver.cs:1617 
   at GooglePlayServices.PlayServicesResolver+<ScheduleResolve>c__AnonStorey1E.<>m__40 () [0x00000] in /Users/smiles/dev/src/unity-jar-resolver/source/PlayServicesResolver/src/PlayServicesResolver.cs:1586 
   at GooglePlayServices.PlayServicesResolver.ExecuteNextResolveJob () [0x00069] in /Users/smiles/dev/src/unity-jar-resolver/source/PlayServicesResolver/src/PlayServicesResolver.cs:1445 
   at GooglePlayServices.PlayServicesResolver.ScheduleResolve (System.Boolean forceResolution, System.Boolean closeWindowOnCompletion, System.Action`1[T] resolutionCompleteWithResult, System.Boolean isAutoResolveJob) [0x000a7] in /Users/smiles/dev/src/unity-jar-resolver/source/PlayServicesResolver/src/PlayServicesResolver.cs:1599 
   at GooglePlayServices.PlayServicesResolver.AutoResolve (System.Action resolutionComplete) [0x00017] in /Users/smiles/dev/src/unity-jar-resolver/source/PlayServicesResolver/src/PlayServicesResolver.cs:1120 
   at GooglePlayServices.PlayServicesResolver.<ScheduleAutoResolve>m__48 () [0x00016] in /Users/smiles/dev/src/unity-jar-resolver/source/PlayServicesResolver/src/PlayServicesResolver.cs:1099 
   at Google.RunOnMainThread.ExecutePollingJobs () [0x0004a] in /Users/smiles/dev/src/unity-jar-resolver/source/VersionHandlerImpl/src/RunOnMainThread.cs:300 
 UnityEngine.Debug:LogError(Object)
 Google.RunOnMainThread:ExecutePollingJobs() (at /Users/smiles/dev/src/unity-jar-resolver/source/VersionHandlerImpl/src/RunOnMainThread.cs:303)
 Google.RunOnMainThread:<ExecuteAll>m__17() (at /Users/smiles/dev/src/unity-jar-resolver/source/VersionHandlerImpl/src/RunOnMainThread.cs:414)
 Google.RunOnMainThread:RunAction(Action) (at /Users/smiles/dev/src/unity-jar-resolver/source/VersionHandlerImpl/src/RunOnMainThread.cs:234)
 Google.RunOnMainThread:ExecuteAll() (at /Users/smiles/dev/src/unity-jar-resolver/source/VersionHandlerImpl/src/RunOnMainThread.cs:406)
 UnityEditor.EditorApplication:Internal_CallUpdateFunctions()

I have been trying to fix this all day, thanks a lot for helping ! :)