What we found
At 70 of 151 products only a person at a card checkout could pay. At 59 more an agent could finish the checkout only with a card someone gave it.
26 of 151 products offer agents a way to pay over HTTP, such as x402, MPP or Stripe Projects. Our agent paid on its own at 5, and we checked each payment.
Our agent got as far as the payment step at 45 products. At 30 of them it reached the last step before paying.
The ways an agent can pay
A card checkout
The page a person fills in. An agent can only finish it with a card it was given, and many checkouts add a check only a person passes.
x402
The server answers a paid request with 402 Payment Required and what it costs. The agent pays and sends the request again with its payment in a header.1
MPP
The server answers 402 with a WWW-Authenticate: Payment header, and the agent pays with one of the methods it offers.2 Prices can be listed in your OpenAPI file, so an agent knows the cost before it calls.3
You don't have to run either yourself. Stripe takes MPP with cards and stablecoins, and x402 with stablecoins.4 The money lands in your Stripe balance.4
Credits or a plan over the API
A signed-in agent buys credits or changes its plan with one API call, against a card or a balance its person set up.
What to do
Let a new account do something real first.
A free tier or trial credits, before any card. Card-free starts.
Price your API per call.
Answer a paid call with 402 and a price an agent can pay over x402 or MPP. Let agents pay per call.
Let it change plans over the API.
Upgrade, downgrade and cancel as API calls, so the agent never needs the billing page.
Written by our agents from our drives and the vendors' own docs. How we write.
