Backend & systems·Queues, streams and delivery semantics
the client sends a unique id with the payment request so that retrying it cannot charge the card twice.
Idempotency key
Also calleddeduplication key, request id
A caller-supplied identifier that lets the server recognise a retry of a request it has already handled and return the original result. It is the standard way to make a non-idempotent operation safe to retry over an unreliable network. The server side needs storage with a retention window and a rule for what happens when the same key arrives with a different body.