Inspect the challenge
A client should verify price, asset, network, recipient, expiry and resource binding before it signs or pays.
AGENT PAYMENT FIELD GUIDE · 2026
x402 Protocol Guide
The x402 Protocol Guide (SKU SML-X402-001, $29 one-time) maps the full machine-payment loop — request → 402 challenge → payment → retry → delivery — and the evidence required between challenge and access: inspect the challenge, authorize narrowly, and keep settlement separate from delivery verification.
Understand the x402 protocol and HTTP 402 payment flow for APIs, content and AI agents: discovery, payment requirements, authorization, settlement and accepted delivery.
SML-X402-001$29 ONE TIMEINSTANT PDF DELIVERY
THE OUTCOME
What is the full x402 machine-payment loop, and what evidence sits between challenge and access?
The x402 loop runs request → 402 challenge → payment → retry → delivery; before paying, the client should verify price, asset, network, recipient, expiry and resource binding, and keep settlement separate from delivery verification.
Use this guide to: Follow the HTTP 402 payment sequence and distinguish spending approval, settlement and API delivery.
WHAT YOU WILL LEARN
What will you learn from this guide?
You will learn the request → 402 → payment → retry → delivery sequence, what clients should verify before authorizing payment, and why settlement and accepted delivery must be verified separately.
- The request → 402 → payment → retry → delivery sequence
- What clients should verify before authorizing payment
- Why settlement and accepted delivery are separate evidence stages
- Operational controls for price, network, recipient, replay and failure handling
INSIDE THE GUIDE
What concepts and decision checks does the guide cover?
The guide covers four operational concepts: inspect the challenge, authorize narrowly, separate settlement from delivery, and retain evidence.
Authorize narrowly
Payment policy should cap amount, restrict destinations and bind approval to the intended request. MCP servers that spend need the same policy — see the MCP payments guide.
Separate settlement from delivery
A successful transfer proves value moved. It does not prove the paid API returned a correct, complete response. The x402 payment protocol keeps settlement and delivery as separate evidence stages.
Retain evidence
Request identifiers, payment evidence, response status and acceptance checks support retries, disputes and audits.
PRIMARY SOURCES
What sources is the guide built on?
The guide is built on the x402 documentation and x402 specification linked below — with source notes inside the PDF itself.
x402 documentation →x402 specification →FAQ
What should buyers know before purchasing?
x402 is an open payment protocol that uses HTTP 402 Payment Required for machine-readable payment terms; the guide provides no wallet, and payment alone never proves delivery.
What is x402?
x402 is an open payment protocol that uses HTTP 402 Payment Required to let services present machine-readable payment terms.
Does the guide provide a wallet?
No. It explains the protocol and operational controls; it does not custody funds or sign transactions.
Does payment prove delivery?
No. Settlement and accepted delivery should be verified separately.
How do you get the PDF?
One-time purchase. Stripe Checkout redirects to the purchased PDF after successful payment.
Buy x402 Protocol Guide — $29Educational information only. No personalized investment, legal, tax, regulatory, cybersecurity or business advice. No ranking, citation, performance or financial outcome is guaranteed.
What is included in this PDF?
4 pages in a fixed-layout PDF: HTTP 402 payment challenges, caller approval and API delivery checks. This is a compact field guide with review checks and source notes.