400 Bad Request · type invalid_request
When it happens
Reserved for endpoints where a duplicate would matter most, such as ones that send documents to a borrower. No endpoint available today requires a key, so you won’t see this code yet.
What to do
Send an Idempotency-Key on every write now, and you’ll never see it. See idempotency.
No endpoint returns this code today. It is registered so that integrations can handle it when it appears.