USDC with x402

x402 is an open HTTP payment standard that turns 402 Payment Required into a machine-readable on-chain payment challenge.

Payment challenge

An unpaid request to a paid endpoint returns the exact price, network, asset, and payment destination. Prices use integer atomic units, not floating-point dollars: 1000000 equals 1 USDC.

Sign & retry

The client builds the quoted Algorand transaction group, signs its transfer, and retries with the PAYMENT-SIGNATURE header. The contributor API key cannot authorize a payment; payment signing needs a wallet or transaction signer.

Verify → work → settle

Verification simulates the group without submitting it. The registry provisions the sandbox or performs the job before asking the facilitator to settle. A startup failure returns an error without settling the payment.

Successful settlement is reported in PAYMENT-RESPONSE. Payer identity comes from the transaction sender.

Integrate a client

Use an x402-capable client or the MCP tools to handle challenges and signing. A plain unpaid curl demonstrates the challenge; it does not execute paid work.

The x402 API covers headers, schemas, client recipes, and errors.