"Just add Stripe" is the default advice for a solo dev who needs to charge money. It works right up until you're an Indian merchant trying to sell to a buyer in San Francisco and a buyer in Bangalore in the same afternoon — at which point you discover that a single provider can't actually do both, and the fix rearranges more of your code than you'd expect. I hit this building Skill Exchange (a marketplace for reusable AI skills — link at the end). The marketplace itself isn't the point here...