Codex Machine Payment Protocol (MPP)

Use this skill when the Codex Supergraph returns a 402 Payment Required response. The MPP challenge flow lets you pay per query without needing an API key.

How it works

1. Send a GraphQL query (no credential).
2. Server returns 402 Payment Required with WWW-Authenticate: Payment ... challenges.
3. Client solves one challenge and retries with Authorization: Payment <credential>.
4. Server returns GraphQL data + Payment-Receipt header.

Constraints