# idempotency_key_required

**HTTP 400** · type `invalid_request_error`

## When

A create, send, or void with no `Idempotency-Key` and no `external_id`.

## Fix

Send one.

## Where it comes from

- `POST /v1/invoices`: Create an invoice
- `POST /v1/invoices/{id}/send`: Send an invoice
- `POST /v1/invoices/{id}/void`: Void an invoice

[All errors](/errors)