# idempotency_key_reused

This Idempotency-Key was already used with a different request. What causes the BioFlow API's idempotency_key_reused error (HTTP 422) and how to fix it.

HTTP 422 · `application/problem+json` · This Idempotency-Key was already used with a different request.

## What causes it

- The `Idempotency-Key` was already used with a DIFFERENT request body or path — keys bind to one logical request.

## How to fix it

- Generate a fresh unique key (e.g. a UUID) for every new logical request; reuse a key only for retries of the identical request.

## Example response body

```json
{
  "type": "https://getbioflow.com/docs/api/errors/idempotency-key-reused",
  "title": "This Idempotency-Key was already used with a different request",
  "status": 422,
  "instance": "urn:request:req_01abc",
  "code": "idempotency_key_reused",
  "request_id": "req_01abc"
}
```

Branch on the stable `code` field — `title` and `detail` are for humans and may
change. `type` (`https://getbioflow.com/docs/api/errors/idempotency-key-reused`) always resolves to this page. Quote
`request_id` when contacting support. Full code registry on the
[API docs hub](/docs/api#errors); the complete surface is in the
[interactive reference](/docs/api-reference).