My soul left my body...

It really is just watching ads constantly. Anyway, whether you pass or not doesn't affect the final coins, So once you enter a stage, just rush through and watch the ads with dead eyes. After 400 coins, you'll be watching double ads with even deader eyes (about 4 ads total including clearing the stage). And you only get a measly 2 coins... Seriously, if you get the hidden mission 550 coins the veterans mentioned, you can probably delete the game. Otherwise, you'll be watching ads endlessly 🙄