Why aren't ads displayed in the app (adMob)?

Question

Android

There is an application for android (alpha stage in google play). Built in ads, registered device testID. Ads in the debug version are shown on my device. Removed testID, published as alpha in google play. The result is that there are no ads on other devices (I can’t check it on my own). What's the catch?
I am also interested in the following - do they pay for ad impressions (both video and banners) or only transitions?

Answer 1

Most likely the problem is in the Fill Rate, ie. AdMob simply doesn't have ads for your app because you don't have a lot of unique users yet.
Use testID to make sure that everything is implemented correctly and wait for the settings and increase in Fill Rate.
Also in AdListener there is an onError method (I don’t remember the exact name of the classes / methods), an error code flies there if it was not possible to load the ad, add logging / breakpoint and see what the problem is.
More details about Fill Rate and problems with it can be googled.