Make "Remove Ads" function. You need to pay 5k diamonds.
If you don't have too much diamonds, you can pay 2k diamonds for one month. So the rest of the diamonds can be payed before one month.
OR 10k. Anyone can pay 5k. And every time you watch an ADS, they earn money. So... They're not adding this. Cause they created a free app, with excellent (i'm italian.) funcionality, and they paid for doing this. And if they don't earn ANYTHING, they can't make the app remain.