x402

x402 is an open standard for paying over HTTP: a server answers 402 Payment Required with what it wants, and the client pays by signing an authorisation instead of sending a transaction. Kite uses it in two places.

At checkout: x402 on payment links

A payment link at /pay/<id> is also an x402 resource. When an agent (or any HTTP client) fetches it:

• With Accept: application/json (or any non-HTML accept header): Kite returns a 402 Payment Required response with the full x402 body — accepts array with payment requirements for every chain that supports x402, plus PAYMENT-REQUIRED header. The agent picks one, signs, and repeats the request with a PAYMENT-SIGNATURE header to pay.
• With Accept: text/html (browsers): Kite serves the checkout page instead.

As a facilitator for your services

Your own API can charge per request with x402 and use Kite as its facilitator. With an API key that has the x402 scope:

Endpoint	Use
GET /api/x402/supported	Which networks and schemes this server can settle.
POST /api/x402/pay	Open a transfer for a quote, to be paid with x402.
GET /api/x402/transfer/{id}/requirements	The payment requirements to send in your 402 response.
POST /api/x402/verify	Check a client’s payment before doing the work.
POST /api/x402/settle	Settle it.

See the API Reference for the request and response shapes.