k4d

Docs

MoonX, PayBox, and x402 for people who still have email.

x402 paywalled API

HTTP already had a status code for "pay me". most of the industry ignored it and built another account system instead. x402 is the correction.

stack

  • open standard: docs.x402.org
  • seller responds 402 with payment requirements
  • buyer (human or agent) returns a payment payload
  • optional facilitator /verify + /settle
  • paybox agents can pay x402 services via MCP (pay_x402, use_service)

k4d tip links today are not x402. they are a USDC tip + unlock cookie. different rail. see tip-link-unlock.

steps (seller mental model)

  1. client GETs a paid resource.
  2. server replies 402 Payment Required with machine-readable payment instructions.
  3. client prepares payment (wallet / agent / facilitator path).
  4. server verifies + settles (locally or via facilitator).
  5. server returns the resource.

official quickstarts: sellers · buyers

agent path

wire paybox MCP, then let the agent use x402 tools against a seller that speaks the protocol. no custom "agent auth" fantasy required.

pitfalls

  • keep docs vendor-neutral. facilitators are interchangeable plumbing, not religion.
  • do not claim k4d paywall is x402 until it actually speaks 402 headers.
  • micropayments still need gas/network reality. testnets are not optional cosplay.

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