I don't think it's as bad as the parent comment makes it out to be to accept payments.
You don't need to register a company, you can act as a sole proprietor. This requires no paper work, fees or filing anything. You would need a bank account but most folks already have one, your personal checking account would work. You can grab and tweak a pre-made privacy policy in less than an hour if you decide to include one.
I'm also pretty sure (I'm not an accountant) the first year you're self employed you won't get penalized for not paying quarterly taxes. Of course you need to still pay taxes in April, but you can deal with that then. Even if that wasn't true, the worst case scenario is you pay a fee for not filing every quarter. If you accepted payments and were making tons of money hiring an accountant wouldn't be an issue and if you were making close to nothing then you wouldn't have any fees since you have to be taxed $1,000 in the year to be on the hook for paying estimated taxes per quarter.
The last point of writing code stands true tho. You would need to implement some type of payment accepting feature into your app. Fortunately accepting monthly or annual payments is fairly generic. Once you've implemented this in any app you can mostly drop it into another app without a huge amount of effort. It would mainly come down to little tweaks and making the UI match your app.