Many apps collect a small fee every time they are used: a builder fee, a fee share or a plan.
Most of us meet money as wages, tips or a resale margin. Each one needs you there, trading another hour.
Software earns another way. A trading app can add a builder fee to every trade. A booking app can charge a small fee per booking. A members app can sell a plan. Someone sets those numbers and someone receives them, and it is usually a company you have never heard of.
Earning Apps lays it out for every app in the catalog: the mechanism, who pays, where it lands and what the owner sets, with the owner kit as evidence. You can learn all of it without buying anything.