How do I pass in a callback delegate from another class?

I'm trying to implement Unity Rewarded video ads. I watched the video by Mike Geig, and he mentions that it would be a good approach to pass in a delegate to be called by the Advertisement.Show callback method, which makes sense to me. Unfortunately I don't have much experience with delegates and I can't understand the error this throws. I'm able to pass in a delegate method from the same "AdShower" class, but not from my external class.

The error is: Cannot implicitly convert type 'AdShower.ResultDelegate' to 'System.Action< UnityEngine.Advertisements.ShowResult>'

 using UnityEngine;
 using System.Collections;
 using UnityEngine.Advertisements;
 
 public class AdShower : MonoBehaviour 
 {
     private string gameID = "";
 
     private string rewardedPlacementID = "rewardedVideo";
 
     public delegate void ResultDelegate (ShowResult result);
 
     void Awake()
     {
         Advertisement.Initialize (gameID, true);
     }
 
     public bool RewardedAdIsReady()
     {
         return Advertisement.IsReady (rewardedPlacementID);
     }
 
     public void TryShowRewardedAd(ResultDelegate theDelegate)
     {
         ShowOptions options = new ShowOptions ();
         options.resultCallback = theDelegate;
 
         if (Advertisement.IsReady (rewardedPlacementID))
             Advertisement.Show (rewardedPlacementID, options);
     }
 }

Here is a snippet from the other class I want to call the "TryShowRewardedAd" Method:

     public void VideoContinueButtonPressed()
     {
         // already confirmed a video is ready
         r.adShower.TryShowRewardedAd(HandleVideoResult);
     }
 
     private void HandleVideoResult(ShowResult result)
     {
         if (result == ShowResult.Finished)
         {
             Continue();    
         }
     }