Ready-made client — a single copy-paste file

A single-file sandbox client with zero dependencies: copy the file into your project and the first payment goes through without reading the rest of the docs.

The files are hosted by this site — byte-for-byte snapshots of the sandbox clients under the drift-check: when a sandbox release changes a file, the check flags it and the snapshot is updated together with the documentation. What is inside — exactly the places where integrations usually break:

1. HMAC-SHA256 v3 signature with test vectors: selftest() runs them before the first network call — two mismatching strings are debuggable locally, a 401 from the server is not.
2. The whole flow: CreateInvoice → AuthorizeInvoice (PIN 1234) → GetInvoice until Processed / PAID — run it with python client.py demo or node client.js demo.
3. Callback signature verification — with an explicit warning that the signature covers only the timestamp, not the body: the state is confirmed by a separate GetInvoice, see “Callbacks”.

Hand the same link to an AI agent — it copies the signature implementation instead of guessing it.