Settle an order

Settle the order — the final lifecycle transition that locks the order's revenue into the ledger and closes it for further edits. Used by automated close-of-day jobs as well as manually by operators when an order has been fully paid for and serviced.

The action is idempotent — settling an already-settled order is a no-op and returns the same order.

Returns 400 Bad Request when the order can't be settled — for example because it has outstanding balance or contains items that haven't been fulfilled. The error message describes the specific reason.