I received policy violation message from AdMob stating that:
Rewarded Ads - Disallowed Rewarded Implementation - Must fix - Rewarded ads may only be served after a user affirmatively opts to view a rewarded ad. Additionally, a user must opt to view each rewarded ad individually and cannot opt-in to automatically seeing rewarded ads.
All I understood from that is I need to write a clear written explanation of what the user will get if he hits the button which I did. I also added play sign on the button to let the user know that the button contains ads.
What I didn't understand is the last part - "...and cannot opt-in to automatically seeing rewarded ads". What does it mean? I asked AdMob team and the only message I repeatedly get from them says pretty much nothing useful. Probably auto-reply.