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

# Idempotency

> Retry message sends without creating duplicate sends.

Use `Idempotency-Key` when sending messages from your backend.

```http theme={null}
POST /api/v1/sessions/{sessionId}/messages
Authorization: Bearer <api_key>
Content-Type: application/json
Idempotency-Key: order-123-ready-v1
```

WADial stores the key with the outgoing message. If you retry the same request with the same key and same content, WADial returns the stored message record instead of sending a duplicate.

If the same key is reused with different message content, WADial returns a `409 conflict`.

Good keys are stable for one business action:

* `order-123-ready-v1`
* `invoice-987-reminder-1`
* `ticket-456-assigned`

Do not use timestamps or random values for retries, because each retry would look like a new send.