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Protocol

HTTP 402 lifecycle

Trace request, challenge, approval, payment proof, retry, and response.

The 402 lifecycle is the same shape for client and agent calls.

Agent summary

  • First request the resource normally.
  • Let pay parse the 402 challenge.
  • Authorize locally when payment is required.
  • Retry with the proof produced by pay.
  • Return the final API response.

Flow

client -> API: request resource
API -> client: 402 Payment Required
pay -> wallet: request local authorization
pay -> API: retry with payment proof
API -> client: 200 OK

Runnable check

pay --sandbox curl https://payment-debugger.vercel.app/mpp/quote/AAPL

Protocol

Understand how pay handles MPP and x402 challenges, payment proofs, and sandbox networks.

MPP

Understand Machine Payments Protocol charge and session challenges.

On this page

Agent summaryFlowRunnable check