We're thinking about starting a fintech company in the space, and we're wondering what the fees are like for users buying stocks etc through an application. Essentially, does Robinhood pay a 30% fee each and every time a user buys a stock?

We've searched through Apple's website and guidelines - https://developer.apple.com/app-store/review/guidelines/, but we're unable to find any clear answers. Could you folks please help?