How it works
Networks fail in the middle of requests. If your call to create an invoice times out, you cannot tell whether the invoice was created. With an idempotency key, the client generates a unique value per intended action and sends it in a header. The server stores the key with the result. If the same key arrives again, it returns the original response instead of creating a second record.
Example
A billing product posts an invoice to a customer's ledger and the connection drops. It retries with the same Idempotency-Key value. The ledger receives one invoice, and the product receives the original invoice id both times.
In integrations
Accounting records are where duplicates hurt most: a doubled payment or bill becomes an audit problem. Unify Int write endpoints are designed to accept an Idempotency-Key header and apply it even when the underlying platform has no idempotency support of its own. Pair it with validation before submit and an audit trail for finance-grade writes. Generate the key from your own record, such as your internal payment id, rather than at random per attempt. That way every retry of the same business action carries the same key, even across process restarts.