> For the complete documentation index, see [llms.txt](https://docs.partssource.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.partssource.com/webhooks/delivery-and-retries.md).

# Delivery & Retries

Headers, delivery semantics, limits, and how to inspect your deliveries

## Delivery headers

| Header           | Content                                              |
| ---------------- | ---------------------------------------------------- |
| `X-PS-Signature` | HMAC-SHA256 of `<timestamp>.<raw body>`, hex-encoded |
| `X-PS-Timestamp` | Unix seconds at send time                            |
| `Content-Type`   | `application/json`                                   |

Signature verification is specified in [Verifying Deliveries](/webhooks/verifying-deliveries.md).

## Delivery semantics

**Delivery is at-least-once.** Duplicates are possible; deduplicate with the composite key from the [Quickstart](/webhooks/quickstart.md) (`event_type:order_id:line_item_id:occurred_at`).

**Ordering is not guaranteed.** An event can arrive before another event that logically precedes it — for example, a shipment-shipped event before the corresponding order-line-created event. Key all state transitions on the event content, not arrival order.

**Respond fast.** Return 2xx within 10 seconds and process asynchronously; slow handlers are treated as failed deliveries.

## Limits

| Constraint          | Value      |
| ------------------- | ---------- |
| Max payload size    | 1 MB       |
| Response timeout    | 10 seconds |
| Timestamp tolerance | 5 minutes  |

## Retries

The retry schedule is being finalized and will be published here once the platform behavior is confirmed. Until then, assume failed deliveries may be retried and keep your handler idempotent — the deduplication key makes this safe.

## Viewing your deliveries

You can inspect delivery attempts at two endpoints (authenticated with your standard API bearer token):

* `GET /v1/webhooks/{webhookId}/deliveries` — recent deliveries with status and attempts
* `GET /v1/webhooks/{webhookId}/deliveries/{deliveryId}` — a single delivery

These are the first stop when deliveries seem to be missing — see [Troubleshooting](/webhooks/troubleshooting.md).


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