And how much would you pay for that? What would be your prefered model? per number of users? per number of API calls? a % transaction fee on top of existing stripe fees? Something else?
As someone else looking for the same thing, I'd pay a monthly subscription on a per number of tiers. I'd likely pay around $10-15 for every 1,000 users, probably a little more. I wouldn't ever do a "% of revenue" or a fee on top of existing transactions.
You should work out the price - asking customers what they want to pay tells you nothing valuable.