What are the things one could be doing wrong if admob ads are not showing up?

What are the things that one could be doing wrong that can cause this problem or ads not showing up? Even though there is enough information on the internet but this problem remains and a lot of people have this issue with no solution and questions unanswered and this is the second thing I wanna know why nobody would like to answer this particular question or help
I included this as a discussion because I need opinions and lots of them and because I looked up all the forums and added my own question but had no luck… and there seems nothing I am doing wrong, not that I actually am not doing something wrong rather I am doing everything I found in the documents and what not… but the problem remains.

Just FYI I have not installed unreal in my C drive but rather in my D drive and the android studio is in C. Which is the last thing I am going to try… after this I don’t know what I can do. Lastly I am trying to test ads on my mobile devices but I am directly coping it from my build folder t in my project directory into my mobile I did uploaded and tested that too but not as much as direct one. So is that the problem