Ok, hear me out. I want to support the development of the game without spending too much money. Not everybody has the privilege to spend money on the game. Of course, the ads need to be non-intrusive, so they shouldn't pop up in the middle of the game because no one likes that.
So, here's the idea that popped into my head: What if there was an NPC that gives you an ad, and as a reward, it gives you points? You can then exchange these points for items like candies or green gems. People often discuss ways of getting free green gems, and I think this solution is pretty good. Lava gets money, and we get gems/items.