@Override
 public void requestInterstitialAd(
     CustomEventInterstitialListener listener,
     Activity activity,
     String label,
     String placement_id,
     MediationAdRequest adRequest,
     Object extra) {
   iav = new InterstitialAdView(activity);
   iav.setPlacementID(placement_id);
   iav.setAdListener(this);
   iav.setShouldServePSAs(false);
   this.listener = listener;
   iav.loadAd();
 }
 @Override
 public void showInterstitial() {
   if (iav != null) iav.show();
 }
 @Override
 public void destroy() {
   if (iav != null) iav.destroy();
 }