NullReferenceException at at GoogleMobileAds.Api.MobileAds.Initialize (System.Action`1[T] initCompleteAction) [0x00000] in <00000000000000000000000000000000>:0

Hello. There is a problem with google AdMob. Test ads are shown in the editor (There are no errors in the editor), but real ads are not showing on my phone. Then I decided to use USB debugging and found out that the following error occurs:

"NullReferenceException: Object reference not set to an instance of an object. at GoogleMobileAds.Api.MobileAds.Initialize (System.Action`1[T] initCompleteAction) [0x00000] in :0 at Show_ads.Start () [0x00000] in :0"

Here's my script:

using GoogleMobileAds.Api; using System.Collections; using System; using UnityEngine.Scripting; [assembly: Preserve]

public class Show_ads : MonoBehaviour { //ADS---------------------------- private RewardedAd rewardedAd; private const string RewardedID = "id"; //ADS----------------------------

 void Start()
 {
     MobileAds.Initialize(initStatus => { });
     LoadRewardedAD();
 }

 private void LoadRewardedAD()
 {
     //load-ad
     rewardedAd = new RewardedAd(RewardedID);
     AdRequest adRequest = new AdRequest.Builder().Build();
     rewardedAd.LoadAd(adRequest);

     rewardedAd.OnUserEarnedReward += HandleUserEarnedReward;
  }
  //Called from another script
 public void ShowRewardedAD()
 {
     if (rewardedAd.IsLoaded())
     {
         rewardedAd.Show();
     }
 }
 public void HandleUserEarnedReward(object sender, Reward args)
 {
     if (Reward_type == 0)
     {
   //gem
     }
     else if (Reward_type == 1)
     {
         //coin

     }
     else if (Reward_type == 2)
     {
         //Respawn

     }
 }

 private IEnumerator WaitAD()
 {
     yield return new WaitForSeconds(3);
     LoadRewardedAD();
 }

}

Who can help?