Increment value and save to PlayPrefs as RewardedAd reward.

What am I doing wrong?

  using UnityEngine;
  using UnityEngine.Advertisements;
  
  public class PlayRewardedVideoScript : MonoBehaviour
  {
      public int markers;
  
      void start()
      {
          markers = PlayerPrefs.GetInt("markers");
      }
  
      public void ShowRewardedAd()
      {
          if (Advertisement.IsReady("rewardedVideo"))
          {
              var options = new ShowOptions { resultCallback = HandleShowResult };
              Advertisement.Show("rewardedVideo", options);
          }
      }
  
      private void HandleShowResult(ShowResult result)
      {
          switch (result)
          {
              case ShowResult.Finished:
                  Debug.Log("The ad was successfully shown.");
                  //
                  // YOUR CODE TO REWARD THE GAMER
                  // Give coins etc.
                  markers += 100;
                  PlayerPrefs.SetInt("markers", markers);
                  PlayerPrefs.Save();
                  break;
              case ShowResult.Skipped:
                  Debug.Log("The ad was skipped before reaching the end.");
                  break;
              case ShowResult.Failed:
                  Debug.LogError("The ad failed to be shown.");
                  break;
          }
      }
  }

Don't understand why this won't increment properly. The console shows that the ad was successfully shown... Many thx.