Why can not I show banner with Google AdMob FireBase Unity Plugin ?

0 down vote favorite I try to show banner with code used in example at this link: https://firebase.google.com/docs/admob/unity/start

Code:

string id = "ca-app-pub-6558685611970079/2868828748";

 BannerView bannewView = new BannerView (id, AdSize.Banner, AdPosition.Bottom);
 AdRequest request = new AdRequest.Builder ().Build ();
 bannewView.LoadAd (request);

IEnumerator Start() { yield return new WaitForSeconds (3.3f); RequestBanner (); } I have the next log in console when I try to start scene in editor:

When I build app, second line(OException: Sharing violation on path ProjectSettings\GoogleAarExplodeCache.xml) logs in console after build on android.

On device app starts but nothing shows. I have my app banner ir in admobs as you can see.

So, what can I do to fix this ?