Optional client-provided idempotency key, scoped to your organization and to this endpoint (the same key sent to other endpoints deduplicates independently). Retrying an identical request with the same key (lost response, timeout, automated retry) returns the wallet created by the original request instead of creating a duplicate. Deduplication is bounded in time: a key is recognized only while the server retains the original request's execution history (a fixed retention window measured in days, not indefinitely), so retry promptly and never reuse a key for a different request — a key reused after the window lapses is treated as new and will create another wallet. Within the window, reuse detection is limited to what the server can observe after the fact: a key that resolves to a different vault or network is rejected with a 409. Differences in other fields (such as name) are not detected — the original request's wallet is returned — so always retry with the identical request body. A key whose creation attempt failed is also rejected with a 409: the failure is terminal for that key, so retry with a new one. With async, the key doubles as the polling handle (see async). An empty value is treated as absent. Ignored for fiat wallets: fiat wallet creation does not deduplicate retries.
