private void onError(AndroidJavaObject ad, AndroidJavaObject error)
        {
            string errorMessage = error.Call <string>("getErrorMessage", new object[0]);

            interstitialAd.executeOnMainThread(delegate
            {
                if (interstitialAd.InterstitialAdDidFailWithError != null)
                {
                    interstitialAd.InterstitialAdDidFailWithError(errorMessage);
                }
            });
        }