Andriod GoogleMobileAds not working in Real Device(Http respose code:400),

Google ads are not working on real device but Test ads are Working FINE in emulator and also in real Device but after Game Release there is not any ads so therefore I have checked logs that prints ][1]

I am struggling on this issue from last 2 days. I have also tried many things as suggested on other posts but nothing helps .I have tried to change ad size to AdSize.SmartBanner .I have also updated sdk .also I have found some people says that google blocks some game from receiving ads but I have not received any mail about it.

SO HERE PLEASE HELP WHAT IS REASON OF THIS ERRORS,