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

# idempotency-key-missing

> An Idempotency-Key header is required.

**Status 400.** An Idempotency-Key header is required.

The response is `application/problem+json`, and its `type` is
`https://docs.andteam.com/api/problems/idempotency-key-missing`:

```json theme={null}
{
  "type": "https://docs.andteam.com/api/problems/idempotency-key-missing",
  "title": "An Idempotency-Key header is required",
  "status": 400
}
```

## What it means

Every POST needs an `Idempotency-Key` header, so a retry never makes a second record.

## What to do

Send a unique `Idempotency-Key` (a UUID works) and reuse it only when you retry the same request. See [Retries and versions](https://docs.andteam.com/guides/idempotency.md).

See [Errors](https://docs.andteam.com/errors.md) for every type.


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