Admob Ad-unit ads serving issue

3-4 days ago I created Ad-unit for my new App but ad-unit is still not serving ads.
Anyone faced similar issue?

Use ad failed to load block to know problem.

Test ads unit are working, problem is with ad mob ad-unit

Check your admob dashboard, is there any restrictions imposed on your account like ad serving limit or any other?

Nothing, no restriction

I created a campaign, ad unit showing campaign ads but not real ads.
Anyone faced this issue?