ADS are not working

so i made a button that shows up after i die saying watch ad. this is the script i used:
using System.Collections;
using UnityEngine.Advertisements;
using UnityEngine;

public class PlayAd : MonoBehaviour
{
public void ShowAd()
{
if (Advertisement.IsReady())
{
Advertisement.Show ("rewardedVideo", new ShowOptions() { resultCallback = HandleAdResult; });
}
}

private void HandleAdResult(ShowResult result)
{
switch (result)
{
case ShowResult.Finished:
Debug.Log("Player gains +5 score");
break;
case ShowResult.Skipped:
Debug.Log("Player did not fully watch ad");
break;
case ShowResult.Failed:
Debug.Log("Player failed to launch ad");
break;
}
}
}


but it doesnt work when i try to play it. p.s ive turned on unity ads
how do i make it work

 

AHHH Thank you