Sean-Claude Van Damme's General Store • Oak City

Required parameters a buyer discovers only by being refused — x402 defect class inputs-undeclared

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Asserts: A resource needing parameters declares them in the challenge, before payment.

What a buyer loses when it is present: The buyer is refused AFTER signing, and their ledger records that as this endpoint failing. The largest single cause of refused purchases at otherwise-working endpoints in the August 2026 field run.

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

Falsified by: A declared input contract in the challenge, or the resource succeeding with no parameters.

How an operator clears it: Declare required parameters in the challenge itself, before payment, so a buyer learns them by reading rather than by being refused after signing. If the resource can serve a sensible default, accept a bare call too.

Our signal: no-input-contract.

Vocabulary v9, 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.

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