Audience question: when a third-party API doesn't support idempotency keys and the find-or-create technique is impractical (thousands of entities, race conditions), what other options guarantee only one item is created? Answer: PUT with a sender-chosen ID (e.g. UUIDv4) if the API allows it; otherwise you're in a 'wrong protocol' situation — compensation is painful and costly. Best to negotiate with the provider, and failing that, consider switching providers.