Operates on Service Orders, shown in the Zuper client app as "Work Order" (in every industry). Work Orders share the exact same underlying schema and endpoints as Purchase Orders / Material Orders; they're distinguished only by the purchase_order_type field (SERVICE_ORDER here) and the /service_orders route prefix. This is a narrower field set than the full PUT update — intended for lightweight edits (title, dates, remarks, vendor/payment term) without resending the whole order. Work Orders (Service Orders) may change vendor (the assigned subcontractor) through this endpoint.