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 subscription is created 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. The subscription signature — a single HMAC-SHA256 pass over SubscriptionProjectID + Now, not the one-time payments formula — with the test vectors: selftest() runs them before the first network call, including the negative ones (reversed concatenation, the obsolete MD5 formula).
2. All five methods: CreateSubscription → ApproveSubscription → GetSubscriptionStatus, plus CancelSubscription and ResendPinCode — run the flow with python client.py demo or node client.js demo.
3. Callback signature verification for SubscriptionStatusNotification — with an explicit warning that the signature covers only SubscriptionProjectID + Now, not the body: confirm the state with a separate GetSubscriptionStatus, see “Callbacks”.

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