MPP: Empty challenge id

A deliberately broken MPP endpoint charging 0.0001 USDC on Base Sepolia.

Pick a protocol

x402 uses its own PAYMENT-REQUIRED header. MPP uses the standard HTTP auth framework, with no facilitator.

x402Coinbase. PAYMENT-REQUIRED and PAYMENT-SIGNATURE headers.MPPTempo and Stripe. WWW-Authenticate: Payment, no facilitator.

New to these? Read what x402 and MPP put on the wire.

Pick a network

Testnets only. Nothing here can move real money.

Network

Asset

USDC, 6 decimals

Set the price

Amounts are atomic units of the asset, so no decimal point.

Amount

= 0.0001 USDC

Scheme

Recipient

Defaults to this network's burn address.

Choose a behavior

Compliant by default. Every deviation is named, and never on by accident.

Behavior

The MPP challenge carries id="". The draft says a server must never send this and a client must reject it, so an accepting parser is out of spec.

Your endpointEmpty challenge id

/api/mpp?quirk=empty-id

Try it

curl -i "https://test402.com/api/mpp?quirk=empty-id"

Returns 402 whose WWW-Authenticate has an empty id parameter. Reference implementations have disagreed with the draft and with each other here.

Response it will return (HTTP 402)

WWW-Authenticate: Payment id="", realm="test402.com", method="evm", intent="charge", request="eyJhbW91bnQiOiIxMDAiLCJjdXJyZW5jeSI6IjB4MDM2Q2JENTM4NDJjNTQyNjYzNGU3OTI5NTQxZUMyMzE4ZjNkQ0Y3ZSIsIm1ldGhvZERldGFpbHMiOnsiY2hhaW5JZCI6ODQ1MzIsImNyZWRlbnRpYWxUeXBlcyI6WyJhdXRob3JpemF0aW9uIiwidHJhbnNhY3Rpb24iXSwiZGVjaW1hbHMiOjYsInBlcm1pdDJBZGRyZXNzIjoiMHgwMDAwMDAwMDAwMjJENDczMDMwRjExNmRERUU5RjZCNDNhQzc4QkEzIn0sInJlY2lwaWVudCI6IjB4MDAwMDAwMDAwMDAwMDAwMDAwMDAwMDAwMDAwMDAwMDAwMDAwMDQwMiJ9", expires="2026-01-01T00:05:00Z"

{
  "type": "https://paymentauth.org/problems/payment-required",
  "title": "Payment Required",
  "status": 402,
  "detail": "test402 challenge",
  "note": "test402 scenario. quirk=empty-id"
}