Idempotency-Key. TTL 24 hours. Same key + same body replays the stored response.
Gift-card money-move operations declare this header in the public OpenAPI. Loyalty customer/points writes required for hashed ld_* keys are a runtime rule and are not yet parameters on those operations in the spec — generated clients and the playground will not send them unless you add the header yourself.
Statuses differ by product:
Who must send it
Use a UUID v4 per distinct operation. Retries of the same operation must reuse the same key.