# idempotency_key_reused

- HTTP status: 409
- Retry: No
- Execution: not started
- Admin needed: no

**Idempotency-Key reused.** Within 24 hours an Idempotency-Key identifies one request: same method, path and body. Sending the key with a different body or to a different operation is refused so a retry can never silently do something else.

## What it means

The API returns HTTP 409 with `error.code` set to `idempotency_key_reused`. The default message is: "This Idempotency-Key was already used with a different request."

## Common causes

- The same key was used for two different operations.
- The body changed between retries.

## How to identify it

Check the response status (`409`) and `error.code` (`idempotency_key_reused`). Branch on `error.code`, not on the message text: messages can be reworded, codes do not change within v1. Log `error.request_id` (also sent as the `X-Request-Id` header) so support can find the request.

## How to fix it

- Use a new key for a new operation. For a retry, send exactly the original request.

## Retry guidance

Sending the request unchanged fails the same way. Fix the cause first (see How to fix it), then send it again.

## Did anything happen?

This request was refused before any call was placed and before anything was charged.

## Idempotency

Generate a new key for the new request. The original request with this key is unaffected.

## Who can fix it

The developer who sends the request can fix it; no administrator action is normally needed.

## When to contact support

If the error persists after the steps above, contact [support@relationsai.com](mailto:support@relationsai.com). See [Support](/resources/support) for what to include (the `request_id`, the time in UTC, the operation, and whether you used a test or live key) and what never to send (API keys, Authorization headers, webhook signing secrets, recording links, transcripts or customer data).

## Example error response

```json
{
  "error": {
    "code": "idempotency_key_reused",
    "message": "This Idempotency-Key was already used with a different request.",
    "details": {},
    "request_id": "req_ot57su2lklzm53wt35jhp5o2",
    "retry": "no",
    "doc_url": "https://docs.relationsai.com/errors/idempotency_key_reused"
  }
}
```

## Operations that can return this error

- [`POST /calls`](/api/calls#place-a-call): Place a call
- [`POST /campaigns`](/api/campaigns#create-a-campaign): Create a campaign
- [`POST /campaigns/{campaign_id}/recipients`](/api/campaigns#add-recipients): Add recipients
- [`POST /campaigns/{campaign_id}/start`](/api/campaigns#start-a-campaign): Start a campaign
- [`POST /campaigns/{campaign_id}/pause`](/api/campaigns#pause-a-campaign): Pause a campaign
- [`POST /campaigns/{campaign_id}/resume`](/api/campaigns#resume-a-campaign): Resume a campaign
- [`POST /campaigns/{campaign_id}/stop`](/api/campaigns#stop-a-campaign): Stop a campaign
- [`POST /contacts`](/api/contacts#create-a-contact): Create a contact
- [`POST /contacts/upsert`](/api/contacts#create-or-update-a-contact-by-phone-number): Create or update a contact by phone number
- [`DELETE /contacts/{contact_id}`](/api/contacts#delete-a-contact): Delete a contact
- [`POST /dnc-entries`](/api/do-not-call-list#add-a-number-to-the-do-not-call-list): Add a number to the do-not-call list
- [`DELETE /dnc-entries/{dnc_entry_id}`](/api/do-not-call-list#remove-a-number-from-the-do-not-call-list): Remove a number from the do-not-call list
- [`POST /webhook-endpoints`](/api/webhook-endpoints#create-a-webhook-endpoint): Create a webhook endpoint
- [`DELETE /webhook-endpoints/{webhook_endpoint_id}`](/api/webhook-endpoints#delete-a-webhook-endpoint): Delete a webhook endpoint
- [`POST /webhook-endpoints/{webhook_endpoint_id}/rotate-secret`](/api/webhook-endpoints#rotate-a-webhook-signing-secret): Rotate a webhook signing secret
- [`POST /webhook-endpoints/{webhook_endpoint_id}/test`](/api/webhook-endpoints#send-a-test-event): Send a test event
- [`POST /webhook-deliveries/{webhook_delivery_id}/retry`](/api/webhook-endpoints#retry-a-delivery): Retry a delivery

See all codes in the [error-code reference](/fundamentals/error-codes).