I have integrated appLovin ads from its documentation in unity https://dash.applovin.com/documentation/mediation/unity/getting-started/integration
and implemented banner ads also. In unity, I can see banner ads but after the build neither it is working on android nor iOS. What could be the issue?
This issue already happened to me. In my case, I just needed to wait for a few days and the ads began working also on the mobile phone.
If you got the "dummy" ads to work and the real ads still not working after a few days so there could be another problem (I had it when I used google ads) - the application must be installed from the google play store and not from the unity editor to the phone. It only works on a non-development build.