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. Rule-engine-based list endpoint — an alternative to the simple filter.* query params on the plain List endpoint, for building complex AND/OR filter conditions. purchase_order_type is enforced as a top-level query field (not injected into filter_rules) so it still binds correctly even when filter_rule_operator is "OR".