# GoCardless Webhooks

GoCardless is a bank debit / recurring payments platform. It sends webhooks as
batches of events (up to 250 per request) in an `events` array, signed with an
HMAC-SHA256 signature in the `Webhook-Signature` header.

## When to Use This Skill

* How do I receive GoCardless webhooks?
* How do I verify the GoCardless `Webhook-Signature` header?
* Why is my GoCardless webhook signature verification failing?
* How do I handle `payments` `confirmed`/`failed`, `mandates` `cancelled`, or `payouts` `paid` events?
* How do I process the GoCardless `events` array idempotently?

## How GoCardless Signs Webhooks

* Header: `Webhook-Signature` — a bare 64-char lowercase hex digest (no `X-`
  prefix, no `sha256=` scheme prefix)
* Algorithm: HMAC-SHA256 over the raw request body, keyed with the
  webhook endpoint secret (from your GoCardless Dashboard)
* Key: use the secret verbatim as a UTF-8 string — do NOT base64-decode it
  even though it looks base64url-ish; decoding it produces a wrong signature
* Encoding: lowercase hex string
* Comparison: timing-safe equality
* Response: return `204 No Content` once the whole batch is accepted; a non-2xx
  (e.g. `498`) marks the delivery failed. GoCardless does not auto-retry —
  redelivery is manual (`POST /webhooks/{id}/actions/retry`). Delivery is
  at-least-once, so keep handlers idempotent on `event.id`.

(Scheme verified 2026-08 against a live sandbox delivery and the official
`gocardless-nodejs` SDK; GoCardless's prose still doesn't name the algorithm.)

Always verify against the raw body — parsing JSON first and re-serializing will
change the bytes and break the signature.

## Verification (core)

Use the official `gocardless-nodejs` SDK where it runs (Node.js). `parse()` verifies
the signature (timing-safe) and returns the events array, throwing
`InvalidSignatureError` when the signature does not match.

```javascript
// Node.js — official SDK (gocardless-nodejs), req.body is the RAW Buffer
const { parse, InvalidSignatureError } = require('gocardless-nodejs/webhooks');

try {
  const events = parse(
    req.body,                                  // raw body (Buffer/string), NOT parsed JSON
    process.env.GOCARDLESS_WEBHOOK_SECRET,     // webhook endpoint secret
    req.headers['webhook-signature']           // Webhook-Signature header
  );
  // signature valid — process each event, then respond 204
} catch (err) {
  if (err instanceof InvalidSignatureError) {
    // signature mismatch — respond 498 (do not process)
  }
}

```

For languages without a GoCardless SDK (e.g. Python/FastAPI), verify manually — same
algorithm, timing-safe compare:

```python
import hmac, hashlib
expected = hmac.new(secret.encode(), raw_body, hashlib.sha256).hexdigest()
valid = hmac.compare_digest(expected, signature_header)  # timing-safe

```

> For complete handlers with tests, see [examples/express/](https://github.com/hookdeck/webhook-skills/tree/main/skills/gocardless-webhooks/examples/express/), [examples/nextjs/](https://github.com/hookdeck/webhook-skills/tree/main/skills/gocardless-webhooks/examples/nextjs/), [examples/fastapi/](https://github.com/hookdeck/webhook-skills/tree/main/skills/gocardless-webhooks/examples/fastapi/).

## Common Event Types

GoCardless events combine a `resource_type` with an `action`. The most common:

| resource_type | action | Triggered When |
| --- | --- | --- |
| `payments` | `confirmed` | Funds confirmed collected from the customer |
| `payments` | `paid_out` | Payment included in a payout to your bank account |
| `payments` | `failed` | Payment failed (e.g. insufficient funds) |
| `payments` | `cancelled` | Payment cancelled before submission |
| `payments` | `charged_back` | Customer charged the payment back |
| `mandates` | `active` | Mandate set up and ready to collect |
| `mandates` | `customer_approval_granted` | Customer authorised the mandate (confirmed live) |
| `mandates` | `cancelled` | Mandate cancelled (e.g. bank account closed) |
| `mandates` | `failed` | Mandate setup failed |
| `mandates` | `expired` | Mandate expired through inactivity |
| `payouts` | `paid` | Payout sent to your bank account |
| `refunds` | `paid` | Refund submitted to the customer |
| `refunds` | `failed` | Refund failed |
| `subscriptions` | `created` | Subscription created |
| `subscriptions` | `cancelled` | Subscription cancelled |

See [overview.md](https://github.com/hookdeck/webhook-skills/blob/main/skills/gocardless-webhooks/references/overview.md) for the full action list per resource type.

## Environment Variables

```bash
# Webhook endpoint secret from the GoCardless Dashboard (Developers → Webhook endpoints)
GOCARDLESS_WEBHOOK_SECRET=your_webhook_endpoint_secret

```

## Local Development

For local webhook testing, run the Hookdeck CLI via `npx` — no install required:

```bash
npx hookdeck-cli listen 3000 gocardless --path /webhooks/gocardless

```

No account required. The CLI creates a guest account on first run and provides a
local tunnel + web UI for inspecting requests. Use port `8000` for the FastAPI example.

## Reference Materials

* [Overview](https://github.com/hookdeck/webhook-skills/blob/main/skills/gocardless-webhooks/references/overview.md) - What GoCardless webhooks are, full event/action list
* [Setup](https://github.com/hookdeck/webhook-skills/blob/main/skills/gocardless-webhooks/references/setup.md) - Create a webhook endpoint and copy the secret
* [Verification](https://github.com/hookdeck/webhook-skills/blob/main/skills/gocardless-webhooks/references/verification.md) - Signature verification details and gotchas

## Examples

* [Express Example](https://github.com/hookdeck/webhook-skills/tree/main/skills/gocardless-webhooks/examples/express/) - Express 5 handler using the GoCardless SDK, with tests
* [Next.js Example](https://github.com/hookdeck/webhook-skills/tree/main/skills/gocardless-webhooks/examples/nextjs/) - Next.js App Router route using the GoCardless SDK, with tests
* [FastAPI Example](https://github.com/hookdeck/webhook-skills/tree/main/skills/gocardless-webhooks/examples/fastapi/) - Python FastAPI handler with manual HMAC verification, with tests