---
title: "A same-origin surface names different payment terms than the 402 — x402 defect class surface-contradicts-challenge"
description: "A same-origin surface names different payment terms than the 402 (surface-contradicts-challenge), an x402 defect class: Every machine-readable surface on the door's own origin that names a price for the probed path — llms.txt by the code-span convention, the OpenAPI document's payment fields, the challenge's own resource URL — names the 402's minimum on its first rail. For MPP, an observed challenge matches at least one advertised alternative on the exact GET operation's named method, intent, amount and currency fields, with the compared terms stable at both bookends; dynamic amount and omitted currency make no assertion. Detectable by an paid probe. A buyer who budgets from the surface it happened to read first — an installed skill, a fetched llms.txt, a client generated from the OpenAPI document — arrives at the till with the wrong number, refuses or overpays, and reports the door as something it is not. This store did exactly that to its own doors in an installed bundle for weeks before a check looked at a number beside a name."
canonical: "https://scvd.store/defects/surface-contradicts-challenge"
url: "https://scvd.store/defects/surface-contradicts-challenge"
term_code: "surface-contradicts-challenge"
defined_in: "https://scvd.store/defects"
data: "https://scvd.store/defects.json"
vocabulary_version: "22"
license: "https://creativecommons.org/licenses/by/4.0/"
---

# A same-origin surface names different payment terms than the 402

`surface-contradicts-challenge` — an x402 defect class.

**Asserts:** Every machine-readable surface on the door's own origin that names a price for the probed path — llms.txt by the code-span convention, the OpenAPI document's payment fields, the challenge's own resource URL — names the 402's minimum on its first rail. For MPP, an observed challenge matches at least one advertised alternative on the exact GET operation's named method, intent, amount and currency fields, with the compared terms stable at both bookends; dynamic amount and omitted currency make no assertion.

**Costs:** A buyer who budgets from the surface it happened to read first — an installed skill, a fetched llms.txt, a client generated from the OpenAPI document — arrives at the till with the wrong number, refuses or overpays, and reports the door as something it is not. This store did exactly that to its own doors in an installed bundle for weeks before a check looked at a number beside a name.

**Detectable:** paid — only a settled payment reveals it

**Falsified by:** For MPP, any advertised alternative matching all named fields, or an unreadable or moving bookend. For x402, the surface, re-read, naming the 402's minimum on the same rail; or the 402 read again on either side of the surface read carrying a different price, which makes the reading moving rather than contradicting; or the surface's number sitting only in prose, which the convention does not read.

**How an operator clears it:** Derive every surface from the one place the price lives, the way this store derives its llms.txt lines from its shelf, and never type a number into a document that a buyer may install and never refresh. Where a surface must be static, put the endpoint path and the dollar amount in one code span so the convention reads it, and publish the date it was last derived.

**What a buyer does:** Budget from the 402, not from the surface you read first: an installed skill, a fetched llms.txt or a generated client can carry a stale number. Before paying, read the challenge's amount and refuse if it is not what you were told, rather than reporting the door as broken.

**Our signal:** `surfaces (the paid single-door audit's section; rows with state read and agrees false, when the bookend did not move; MPP: surfaces.mpp.rows with state differ under its cited reading rule)`

---

Vocabulary v22, CC BY 4.0. Every class: https://scvd.store/defects. Machine-readable, with falsifiers and cross-instrument mappings: https://scvd.store/defects.json.

A class describes a property of one endpoint at one moment and never accumulates into a judgment on an operator.