Order cancelled (Snapcaster → Platform)

Sent when an Order (or a subset of its lines) is cancelled pre-ship, regardless of initiator: the echo back to the Platform whose own `POST …/cancel` caused it is harmless under `event_id` dedup. Reuses the `order.created` envelope, signing, and delivery semantics (see https://developers.snapcaster.ca/guide/webhook-signing and https://developers.snapcaster.ca/guide/path-b#delivery-semantics). Routed only to order-family Subscriptions (`orders` / `both`); inventory-family Platforms receive the compensating positive `inventory.adjusted` instead. No ordering guarantee: an `order.cancelled` may arrive before its Order’s `order.created` retry. Reconcile on `order_id`.

Delivery payload

The signed `order.cancelled` event.

{
  "event_id": "evt_sandbox_01K4A9CJK1F6S8M3Y2G5T7Q0PV",
  "type": "order.cancelled",
  "created_at": "2026-09-04T19:05:00.000Z",
  "data": {
    "order_id": "ord_sandbox_01K4A8Y6D4QJH2N3P5R7S9T0VW",
    "seller_id": 42,
    "lines": [
      {
        "sku_id": 427286,
        "external_ref": "platform-listing-1042",
        "quantity": 1
      }
    ]
  },
  "api_version": "2026-07"
}

Signature headers

Field	In	Type	Constraints	Meaning	Example
`X-Snapcaster-Timestamp`required	header	string	None	Unix seconds when the request was signed; reject if outside a ±5 minute window.	`string` (generated)
`X-Snapcaster-Signature`required	header	string	None	`sha256=` + lowercase hex of HMAC_SHA256(signingSecret, timestamp ‖ raw request body).	`string` (generated)

Envelope fields

Field	Type	Constraints	Meaning	Example
`event_id`required	string	None	Globally unique, stable across retries; the idempotency/dedup key (STABLE).	`evt_sandbox_01K4A9CJK1F6S8M3Y2G5T7Q0PV`
`type`required	string	allowed values: order.cancelled	Event discriminator (STABLE).	`order.cancelled`
`created_at`required	string	None	ISO-8601 UTC instant of the Cancellation itself, not the Order’s creation (STABLE).	`2026-09-04T19:05:00.000Z`
`data`required	object	None	The operation or event payload.	`{ "order_id": "ord_sandbox_01K4A8Y6D4QJH2N3P5R7S9T0VW", "seller_id": 42, "lines": [ { "sku_id": 427286, "external_ref": "platform-listing-1042", "quantity": 1 } ] }`
`api_version`required	string	allowed values: 2026-07	The dated partner API version this payload was serialized at: the version frozen when the delivery was enqueued (never the live pin), so every retry carries the same value and byte-identical bytes. Added additively per the tolerant-reader rule; see https://developers.snapcaster.ca/guide/api-versioning (STABLE).	`2026-07`

Receiver response

200 - Receiver acked. Return any 2xx after durably accepting the event (verified + persisted/enqueued).