Live demo
Try to double-charge me
This is the hero diagram, running for real. Fire a payment webhook at this site and watch the pipeline verify, queue and settle it — then fire the same event again and watch idempotency refuse the double charge.
Sandboxed: no gateway is called and the money is fiction. Everything else is real — the HMAC verification, the idempotency lookup and the queue are genuine code, and settlement runs on this site's own queue worker. Events are deleted within the hour.
Nothing fired yet. Press the first button and watch the pipeline work.