For anyone with admob ad issue, please make sure use test ad unit before you published it to app store. Using real ad unit Id in test app is against admob policy, your app could be banned by admob without your knowledge
Sample ad units
The quickest way to enable testing is to use Google-provided test ad units. These ad units are not associated with your AdMob account, so there's no risk of your account generating invalid traffic when using these ad units. Here are sample ad units that point to specific test creatives for each format:
Admob official test  ad unit ID
Banner: ca-app-pub-3940256099942544/6300978111
Interstitial: ca-app-pub-3940256099942544/1033173712
Sent from my ONEPLUS A6003 using AppYet Demo
Sent from my ONEPLUS A6003 using AppYet Demo