I think the answer is probably like most things: it depends.

- If the external service supports idempotent operations, use that option.

- If the external service doesn't, but has a "retrieval" feature (i.e. lookup if the thing already exists, e.g fetch refunds on a given payment), use that first.

- If the system has neither, assess how critical it is to avoid duplicates.

Use something like Temporal

You proxy those api calls yourself and have idempotency to cover you for those APIs that don’t have it. If you architect it right you won’t have more than a ms latency addition. You can avoid the race condition issues by using atomic records so if something else tries they’d see it’s in progress and exit.