Send a unique idempotency key per logical write operation, and reuse the same key for any retries of that operation:
X-Idempotency-Key: <partner-generated-uuid>
Safe retries with the same key return the same outcome without duplicate side effects. Generate a new key only when starting a new operation — not on every HTTP retry. Keys will be stored in a shared connect_idempotency_keys table (qualifi-api via internal-router).