# invalid_idempotency_key

> The Idempotency-Key (or `transaction-id` header) is longer than 255 characters or holds non-printable characters. Nothing was changed.

Source: https://tickwire.io/docs/errors/invalid_idempotency_key/

HTTP 400. Nothing reached the broker.

**Likely cause:** A key built from long ids, or one carrying control characters, tabs or bidi marks.

**What to do:** Send 1 to 255 printable characters. Keys are never truncated, so two long keys can't collide.

**Retry:** No. The same request gets the same answer; change something first.

Listed under [Orders and idempotency](https://tickwire.io/docs/errors/#orders-and-idempotency) in [Errors](https://tickwire.io/docs/errors/). Send the error's `requestId` to support and we can find the request.