I think you integrate with their Stripe account (you have to anyway to set up billing/subscriptions anyway), and each month generate a report on how much they b

I think you integrate with their Stripe account (you have to anyway to set up billing/subscriptions anyway), and each month generate a report on how much they billed, then bill their credit card 3% of that. If they don't pay then their site/product shuts down (after a grace period obviously).