Unity Levelplay does not work on mobile testing device. How can I fix this?

I’ve been working and researching for/on this for hours now and I seem to be losing my sanity.
I want to do the Ads Integration through Unity LevelPlay aka IronSource and nothing is working out. There’s no good doc.

I’m at a point where I have an AdsManager without Compiling Errors, a with Ironsource connected testing device and the IronSource Plugin installed in my game. Everything’s ready, but when testing Levelplay/Ironsource doesn’t seem to even exist in my game.

Though I don’t have a lot of experience, I really put a whole lot of blood sweat and tears into this (a lot of tears haha). Please help me, someone.