Payments glossary
x402
x402 is an open payment protocol built into HTTP itself, reviving the 402 "Payment Required" status code. A server quotes a price in the 402 response; the client - commonly an AI agent - pays and retries the request. The protocol is stewarded under the Linux Foundation.
How an x402 payment flows
A client requests a resource - an API call, a dataset, an article. The server responds with HTTP 402 and a machine-readable quote: the price, the accepted payment rail, and where to pay. The client pays programmatically, then repeats the request with proof of payment attached; the server verifies it and returns the resource. No sign-up form, no stored card, no human in the loop - payment becomes a native step in an HTTP conversation.
Why machines needed a new payment protocol
Every existing checkout assumes a person is present: forms to fill, challenges to pass, redirects to follow. AI agents cannot do any of that, and the payments they make are often far too small for card economics to carry. x402 answers both problems with machine-readable pricing and programmatic settlement - and its stewardship under the Linux Foundation keeps the protocol open and neutrally governed rather than owned by any one payments company.
x402 in the agentic stack
x402 handles how a machine pays; protocols such as AP2 handle whether it was authorised to. Together they form the emerging infrastructure of agentic commerce. LekkaPay's agentic payments capability is in development - the approach is documented at /agentic/.
Frequently asked questions
What does the 402 status code have to do with x402?
HTTP reserved status code 402 "Payment Required" in the 1990s, but it was never standardised for real use. x402 finally gives it a job - the server replies 402 with machine-readable payment instructions, and the client pays and repeats the request with proof of payment attached.
How are x402 payments settled?
The protocol is designed to be payment-rail agnostic, but early implementations commonly settle in stablecoins, whose instant, programmable transfers suit machine-speed payments and amounts too small for card economics.
Who is x402 for?
API providers charging per request, publishers charging AI agents for access to content, and agents that need to pay for resources autonomously - without accounts, API keys or a human clicking through a card checkout.
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