MPP challenge with no usable intent — x402 defect class mpp-intent-unregistered-or-missing

Asserts: The intent parameter is present and is either a drafted intent (charge, subscription) or one implementers advertise (session).

What a buyer loses when it is present: Without an intent a client cannot tell a one-off charge from a recurring commitment; a client that guesses charge on a subscription challenge signs for more than it meant to.

Detectable: by an unpaid probe — a GET nobody paid for can see it.

Falsified by: The challenge naming a drafted or widely advertised intent at the stated moment.

How an operator clears it: Name the intent on every challenge; charge for a one-off, subscription for recurring; if you advertise session, know that it has no draft and a registry-only client cannot pay it.

What a buyer does: Do not sign against a challenge whose intent you do not recognise: you cannot know whether you are committing once or repeatedly. Refuse, and say which intent you could not read.

Our signal: mpp-intent-registered.

Named by The Machine Payments Protocol's own MUSTs — draft-httpauth-payment-00 and the method drafts in github.com/tempoxyz/mpp-specs, read at main 2026-09-03. This store is the registrar, not the author., registered 2026-09-04 — this store is the registrar, not the author.

Vocabulary v11, CC BY 4.0. Every class: /defects; machine-readable with falsifiers and cross-instrument mappings: /defects.json. A class describes a property of one endpoint at one moment and never accumulates into a judgment on an operator.