"Hey J, why can't I upgrade to PRO on the COSO mobile app, or why don't you just charge for the app?"

a). The app is not only free but also ad-free.

b). The app stores take a cut of all charges, including in app-purchases - especially Apple.

c). If I offered either of the above they want my personal details. If I'm not handing them yours, they're sure as fuck not having mine.

https://www.macrumors.com/2024/10/17/developers-eu-app-store-trader-requirements/