> ## Documentation Index
> Fetch the complete documentation index at: https://docs.batchrelay.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Idempotency

> Avoid duplicate print-order creation with idempotency keys.

Send an `Idempotency-Key` header with every create request:

```http theme={null}
Idempotency-Key: order_2026_0001
```

Batch Relay stores the first order created for an API account and idempotency key. Replays return the original order record instead of creating a duplicate.

## Recommended keys

Use a stable value from your system:

* Order ID
* Workflow run ID
* External job ID
* n8n execution ID plus item ID

Do not reuse the same idempotency key for different payloads.