# 400 invalid_idempotency_key

**The Idempotency-Key header must be 1 to 255 bytes of visible ASCII (0x21 to 0x7E).**

- HTTP status: 400
- Problem identifier (`type` field): `https://noryo.app/problems/transactions/invalid_idempotency_key`

[← Errors — Transaction Intelligence](https://developer.noryo.app/en-GB/transaction-intelligence/errors)

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Canonical page: https://developer.noryo.app/en-GB/transaction-intelligence/errors/invalid_idempotency_key