Admob rewarded video ad not working

Hi,
The admob rewarded video ad sometimes shows in full screen mode and the user has to either press the device back button or close the app to return to get the reward, other times it doesn’t show the countdown timer (30 seconds).

The game is created by Corona SDK version 2020.3567

is there anyone know how to solve this issue

Thanks.

Just to be clear. You’re saying that live adMob rewarded ads are not working?

I ask, becaue rewardedAds don’t work in test mode.

https://docs.coronalabs.com/plugin/admob/load.html#overview

Yes I make sure that it is live and testMode is false as well
Actually the rewarded video Ad is showing but the issue is in the full screen and the countdown timer not showing.