C# Unity Admob reward not rewarding

this is my first time adding admob to my game.
Rewarded video can show ads video but didn’t rewarding after watching until finish.
its like HandleRewardBasedVideoRewarded didnt work.

public void Start()
{
    // Initialize the Google Mobile Ads SDK.
    MobileAds.Initialize(initStatus => {});
    //MobileAds.initialize(this);
    this.rewardBasedVideo = RewardBasedVideoAd.Instance;
    this.RequestRewardBasedVideo();
    rewardBasedVideo.OnAdRewarded += HandleRewardBasedVideoRewarded;
    PisauScript.adskeluar = PlayerPrefs.GetInt("AdsKeluar", PisauScript.adskeluar);
    if (PisauScript.adskeluar >= 1)
    {
            RequestInterstitial();
    }
 
}


public void HandleRewardBasedVideoRewarded(object sender, Reward args)
{
    revive.NambahNyawa();
}


public void RequestRewardBasedVideo()
{
    //rewardBasedVideo = RewardBasedVideoAd.Instance;
    AdRequest request = new AdRequest.Builder().Build();
    this.rewardBasedVideo.LoadAd(request, Video_AD_ID);
}

public void ShowVideoRewardedAd()
{
    if (rewardBasedVideo.IsLoaded())
    {
        rewardBasedVideo.Show();
    }
}

}