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. If email is provided, sends the order by email and returns a JSON success message. If email is omitted, the response is instead a raw PDF (or Excel, if send_excel is true) binary stream, not JSON.