# idempotency_key_reused — Postify API error

HTTP 422 · Idempotency key reused with a different request body

This page is the resolution of the problem `type` URI `https://usepostify.com/docs/api/problems/idempotency-key-reused`.

This Idempotency-Key was already used within its 24-hour window with a DIFFERENT request body. Keys uniquely identify one logical request; reusing one for different content is always a client bug, so the API refuses rather than guessing.

## Common causes

- A static or hardcoded key is reused across different posts.
- The body is re-serialized differently between attempts (field order is fine; changed values are not).
- A key-generation collision (e.g. truncated hash).

## How to fix

- Generate one fresh key (a UUID) per logical create, and reuse it only for byte-equivalent retries of that same create.
- Persist the key alongside your outbound job so retries reuse it deliberately.

## Example response

```json
{
  "type": "https://usepostify.com/docs/api/problems/idempotency-key-reused",
  "title": "Idempotency key reused with a different request body",
  "status": 422,
  "code": "idempotency_key_reused",
  "detail": "This Idempotency-Key was already used with a different request body.",
  "request_id": "req_6f1f8a2b40d34cd2a6f1e2c9b8d7a601"
}
```

## Related

- [Idempotency docs](https://usepostify.com/docs/api#idempotency)
- [createPost](https://usepostify.com/docs/api-reference/posts/createPost)