Idempotency

When creating payments or cashout orders:

1. You must account for timeouts and retries.
2. If the create API times out or returns a non-200 status, query the status API first before concluding failure.
3. When orderStatus is unavailable, do not infer the order status.
4. Idempotency is valid for 3 months: within the validity period, resubmitting the same merchant order number returns the first accepted result and does not create a duplicate order.
5. Cashin and cashout idempotency are independent of each other: a merchant order number already submitted for cashin can still be submitted for cashout; the same order number only needs to be unique within the same business direction.

These rules already appear in production cashin / cashout notes.