---
title: "Developers — Fynex Help"
description: "The API, webhooks, payment and payout statuses, and error codes."
url: "/docs/developers/"
---

# Developers

The API, webhooks, payment and payout statuses, and error codes.

- [How do I verify Fynex webhook signatures?](/docs/developers/how-do-i-verify-fynex-webhook-signatures/) — Every webhook is signed. Recompute an HMAC-SHA256 of the timestamp and raw body with your signing secret, compare it to the X-Fynex-Signature header, and reject anything older than 5 minutes.
- [Which webhook events does Fynex send?](/docs/developers/which-webhook-events-does-fynex-send/) — Fynex sends events for payments, payment links, subscriptions, promo codes, and business verification. Each has the same envelope, is signed, and retries up to 3 times to allowlisted URLs.
- [How do idempotency keys work?](/docs/developers/how-do-idempotency-keys-work/) — Send a unique idempotency key with a request so a retry can't create a duplicate. Reusing a key returns the original result instead of acting twice — essential for payouts.
- [Payment statuses reference](/docs/developers/payment-statuses-reference/) — The statuses a payment moves through, from created to settled, plus the refund and failure states — with what each one means for your integration.
- [Payout statuses and failure codes reference](/docs/developers/payout-statuses-and-failure-codes-reference/) — The statuses a payout moves through, the approval state, and the failure codes you may receive — each with a customer-safe meaning.
- [How do I test subscriptions with the test clock?](/docs/developers/how-do-i-test-subscriptions-with-the-test-clock/) — A test clock lets you fast-forward time in test mode so you can see a subscription's renewals, trial ending, and dunning without waiting real days.
- [Payment Links API quickstart](/docs/developers/payment-links-api-quickstart/) — Create a payment link over the REST API, share the hosted URL, and receive a webhook when it's paid. Authenticate with your seller account token.