---
title: "MPP challenge naming a method no client can build — x402 defect class mpp-method-unregistered"
description: "MPP challenge naming a method no client can build (mpp-method-unregistered), an x402 defect class: The method parameter names a payment method the specification repository holds a draft for (card, evm, hedera, lightning, nearintents, solana, stellar, stripe, tempo, usdc). Detectable by an unpaid probe. A buyer holding the registry has no credential shape to construct; the refusal lands on the buyer's machine and the seller never learns a buyer came."
canonical: "https://scvd.store/defects/mpp-method-unregistered"
url: "https://scvd.store/defects/mpp-method-unregistered"
term_code: "mpp-method-unregistered"
defined_in: "https://scvd.store/defects"
data: "https://scvd.store/defects.json"
vocabulary_version: "22"
license: "https://creativecommons.org/licenses/by/4.0/"
---

# MPP challenge naming a method no client can build

`mpp-method-unregistered` — an x402 defect class.

**Asserts:** The method parameter names a payment method the specification repository holds a draft for (card, evm, hedera, lightning, nearintents, solana, stellar, stripe, tempo, usdc).

**Costs:** A buyer holding the registry has no credential shape to construct; the refusal lands on the buyer's machine and the seller never learns a buyer came.

**Detectable:** unpaid — a free probe can see it

**Falsified by:** The method appearing as a draft under specs/methods at the stated read date, or a published client building a credential for it.

**How an operator clears it:** Name a method the drafts define, spelled lowercase exactly; if your method is your own, publish its credential shape where clients read and expect the registry to move before buyers do.

**What a buyer does:** Do not guess a credential shape for a method you do not recognise: a signature over the wrong payload is money sent under terms neither side agreed to. Refuse, and name the method you could not build.

**Our signal:** `mpp-method-registered`

---

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.