Why are there no ads appearing in my app?

[foz]

I usually develop and publish ready-made projects. In fact, I have two published applications, but whenever I try to add ads to the book reading app I purchased or create a new project with AdMob for ads, the ads only show for a week and then disappear. I waited for 4 - 5 months in the hope that it would improve over time or would be resolved after a certain period, but it did not. Because of this issue, I am unable to publish the app on the Play Store. Can you help me find a solution to this problem? Are there any alternative ad platforms to AdMob that I could use? Also, could it be that AdMob is not showing ads in the app due to copyright issues related to the presence of books in the application?