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

When a customer chooses Connect wallet, checkout asks Kite to pay the link with x402. Kite answers 402 with a PAYMENT-REQUIRED header, the customer’s wallet signs a transfer authorisation (EIP-3009), and checkout sends it back in a PAYMENT-SIGNATURE header. Kite submits it, moving the customer’s tokens into the transfer’s address, and settles. The customer pays no gas.

It’s offered when the chain’s settlement token supports EIP-3009, such as USDC.

Once Kite accepts an x402 payment, the transfer is x402Settled and settles like any other. If settlement then fails, the funds are held for you to resolve by hand rather than refunded automatically, because the authorisation was already used.

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.