Idempotency key reused with a different request

idempotency_key_reused HTTP 409

An Idempotency-Key was reused with a different request body. The whole point of the key is that one key means one operation, so we refuse rather than guess which one you meant. Retrying an identical request with the same key is safe and returns the original result; a genuinely new operation needs a new key.

How to react to this in code

Switch on the code member — idempotency_key_reused — which is stable. Do not parse the type URI: it points here, and where "here" is may change.