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

# IDEMPOTENCY_KEY_INVALID

> The `Idempotency-Key` header isn't 1 to 255 printable ASCII characters.

`400 Bad Request` · type `invalid_request`

**When it happens**

The `Idempotency-Key` header is empty, longer than 255 characters, or contains characters outside printable ASCII.

**What to do**

Use a UUID v4 (36 characters). See [idempotency](/guides/idempotency).

## Example

```json 400 Bad Request theme={null}
{
  "error": {
    "type": "invalid_request",
    "code": "IDEMPOTENCY_KEY_INVALID",
    "message": "Idempotency-Key must be 1–255 printable ASCII characters.",
    "param": "Idempotency-Key",
    "doc_url": "https://docs.bridgelinepf.com/errors#IDEMPOTENCY_KEY_INVALID",
    "request_id": "req_8fJ2kQ9xLm4TzW7nB3cY5pDv"
  }
}
```

See all [error codes](/errors), or how to [handle errors](/guides/errors).


This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.