VRAd vrAd;
void Start () {
  vrAd = new VRAd (AD_SPACE_ID);  // Replace your Ad Space ID
  vrAd.AdStatusChanged += OnAdStatusChanged;
}
...
void OnAdStatusChanged(object sender, AdStatusChangedEventArgs e) {
  if (vrAd.IsLoaded ()) {
      vrAd.Show (Mode.Off);  // Cardboard mode
  }
}

// Replace with your Ad Space ID
vrAd = VRAd(adSpaceID: ADSPACE_ID, viewController: self, listener: self)
...
func adStatusChanged(withAd ad: VRAd, andStatus adState: AdState) {
  if vrAd.isLoaded()
      vrAd.show(cardboardMode: .Off)  // Cardboard mode
}