You build things for other people.
You can put together a workflow that solves someone's actual problem in an afternoon. What you don't want is to run infrastructure, or a business, in order to sell it to them.
How that works here
Build it once
Compose it in the builder, export the whole thing as a bundle, and import it into someone else's site.
It runs on their account
Their site, their usage, their bill. You are not the middleman for someone else's invoice.
Sell it more than once
List a workflow, a custom node or a compiled action on the marketplace and take a share of each sale.
What is honestly not there yet
Selling directly to someone you already know — a private link rather than a public listing — is not built. Neither is an ongoing cut of what a buyer uses over time, as opposed to a one-off sale; and seller payouts are computed but not yet paid out. If you are weighing this up as income, weigh it up knowing that.
Have a look at the builder.
It costs the same as any other site while you are working out whether it fits.