idempotency_key_reused
That `Idempotency-Key` was already used with a different payload. The key identifies one specific operation, so reusing it for another would make replay meaningless. An `external_id` already issued that is resent with a different type or total in `POST /v1/companies/{company}/invoices` does not return this error but the 409 `unattended_replay_mismatch`.
| Code | Type | HTTP | Category |
|---|---|---|---|
idempotency_key_reused | idempotency_error | 422 | Idempotency |
Cause
That Idempotency-Key was already used with a different payload. The key identifies one specific operation, so reusing it for another would make replay meaningless. An external_id already issued that is resent with a different type or total in POST /v1/companies/{company}/invoices does not return this error but the 409 unattended_replay_mismatch.
What to do
Use a fresh key for each distinct operation, and reuse a key only to retry the exact same request.