unity ads only shows up to 8 ads in a row in my app

Hello, I have a problem with unity ads in my game. In my game I have a button that when clicked shows an ad and gives the user coins. For some reason the ads only work between 6-8 times in a row. And only begin to work again a few hours later. Here is the code for the button:

  using UnityEngine;
  using System.Collections;
  using UnityEngine.Advertisements;
  public class WatchUnityAd : MonoBehaviour
  {
      public int numOfCoinsToAdd = 5;
      bool paused = false,CRRuning = false;
      // Use this for initialization
      void Start()
      {
           //Advertisement.Initialize("66223",false);
      }
  
      public void ShowAd(string zone = "")
      {
  #if UNITY_EDITOR
          StartCoroutine(WaitForAd());
  #endif
          if (string.Equals(zone, ""))
              zone = null;
          /*while (!Advertisement.isInitialized)
          {
              Advertisement.Initialize("66223", false);
          }*/
          ShowOptions options = new ShowOptions();
          options.resultCallback = AdCallbackhandler;
  
          if (Advertisement.IsReady())
              Advertisement.Show(zone, options);
      }
  
      void AdCallbackhandler(ShowResult result)
      {
          switch (result)
          {
              case ShowResult.Finished:
                  Debug.Log("Ad Finished. Rewarding player...");
                  int coinTotal = PlayerPrefs.GetInt("coinTotal");
                  coinTotal += numOfCoinsToAdd;
                  PlayerPrefs.SetInt("coinTotal", coinTotal);
                  gameObject.SetActive(false);
                  break;
              case ShowResult.Skipped:
                  Debug.Log("Ad skipped. Son, I am dissapointed in you");
                  break;
              case ShowResult.Failed:
                  Debug.Log("I swear this has never happened to me before");
                  break;
          }
      }
  
      IEnumerator WaitForAd()
      {
          float currentTimeScale = Time.timeScale;
          Time.timeScale = 0f;
          yield return null;
  
          while (Advertisement.isShowing)
              yield return null;
  
          Time.timeScale = currentTimeScale;
      }
  }

I initialized the ads in a different script on startup. My game is already on the google play store and I wish to fix this problem as soon as possible. So if anyone has any idea for what is causing this please, I need your help. Thank you!