# idempotency_key_required

Starting a run needs an Idempotency-Key header.

## What happened

`POST /runs` takes an `Idempotency-Key` header of 1 to 200 visible characters, so that a retry can never start a second run. A request without one, or with one that is not made of visible characters, is refused with 400.

## What to do

Send a new unique value in `Idempotency-Key` for every run you mean to start, and send the same value only to retry that run.

## Example

```json
{
  "error": {
    "code": "idempotency_key_required",
    "message": "Send an Idempotency-Key header of 1 to 200 visible characters.",
    "detail": {
      "request_id": "3c6f9a52-8e1d-4b7a-9f20-6d41a8c5e7b3"
    }
  }
}
```