Ads. There are so many f-ing ads in the app.

Also referral links. I personally was shocked by this too since I never use them - but I recently saw the money coming in from someone I know with a truly microscopic Youtube channel - somehow people use it and it actually is shockingly profitable

I had 1k sats payed out from smiles recently - it takes forever to get only 1k sats, which isn't a lot.

I bet smiles is very profitable for the makers