* Ability to continue and play solved puzzles till the end by exporting to an external chess app using FEN or PNG
* Bookmark interesting games to come back and maybe solve again (with no points)
...so it requires logging in with a Google account. That means I won't be able to buy the app on my phone
A one-time purchase for an offline privacy-friendly app is 100% fair and the price point and free tier seem great to me (someone upthread said it's like 4.7€ if you want more than 7 puzzles per day iirc), but please just add an option to send you money directly via e.g. IBAN. It's one of the few privacy-friendly options and you also get to keep all of the money
Most other options cut people out: paypal doesn't work half the time ("sorry, something went wrong" when the algorithm hates you today), stripe has issues when your bank and residence country don't match, credit card requires a good credit score, etc. It's all data- and algorithm-based, whereas banks are legally obliged to give you a functional account because it underpins so much of society nowadays. I'd be happy to pay for the app even without using it as a way to add my 'two cents' and hopefully make this more worth your time