I would suggest not wasting your time on this. Look at what happened to me after implementing with Unity Read my post:
https://groups.google.com/g/google-admob-ads-sdk/c/b-pUkBu_qgE
I spend lots of time perfecting it, having very nice placements in my 3d world. It started to make money and they decided to mark all my players clicks as invalid. Not 50%, not 80% but 100% of all my players clicks are not paid for. All my players who clicked the ads go download other games, and I get paid nothing for sending them away from my game.