> ## 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_REQUIRED

> This endpoint requires an `Idempotency-Key` header. No current endpoint does.

`400 Bad Request` · type `invalid_request`

**When it happens**

Reserved for endpoints where a duplicate would matter most, such as ones that send documents to a borrower. **No endpoint available today requires a key**, so you won't see this code yet.

**What to do**

Send an `Idempotency-Key` on every write now, and you'll never see it. See [idempotency](/guides/idempotency).

<Note>No endpoint returns this code today. It is registered so that integrations can handle it when it appears.</Note>

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.