Why does my project build successfully but crash on start in a device?

If you have AdMob set up as an ad network, a scenario might occur where your project builds normally but crashes on start in a device. This can happen due to the AdMob adapter settings in your project. In your project, go to Edit > Project Settings > Services > Mediation, and check if the AdMob app IDs are set properly.

For more information, see Configuring Ad Sources.