Vungle ads not available

When trying to play Vungle ads, I always get a message Ad unavailable: No cached or streaming ad available

from the methodonAdUnavailable()

What puzzles me is that it worked and now it doesn't. It still works on devices where the old version of my app is installed, but when I build it now, it just says that ads are not available.

I am implementing Vungle according to their basic instructions:

final VunglePub vunglePub = VunglePub.getInstance();

@Override
protected void onCreate (Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    vunglePub.init(this, APP_ID);
    vunglePub.setEventListener(vungleListener);
}

private final EventListener vungleListener = new EventListener() {

    @Override
    public void onVideoView(boolean isCompletedView, int watchedMillis, int videoDurationMillis) {
        // Called each time a video completes. isCompletedView is true if the video was not skipped.
    }

    @Override
    public void onAdStart() {
        // Called before playing an ad
    }

    @Override
    public void onAdEnd() {
        // Called when the user leaves the ad and control is returned to your application
    }

    @Override
    public void onCachedAdAvailable() {
        // I don't get this any more
        Log.i("vungle","cachedAdAvail");
    }  

    @Override
    public void onAdUnavailable(String arg0) {
        //I get this when I try to play the ad
        Log.i("vungle","Ad unavailable: "+arg0);
    }

};  

public void playVungleAd() {
    vunglePub.playAd();
}

      

        
        
        
      

    

APP_ID

correct (when I use the wrong id, I get a specific error) and an internet connection is available on the device (AdMob interstitials are working fine, and so is the internet in general).

I don't know what to try more, I have no ideas.