Operates on Subcontractors, shown in the Zuper client app as "Subcontractor" (in every industry). Subcontractors share the exact same underlying schema and endpoints as Vendors / Suppliers; they're distinguished only by the vendor_type field (SUB_CONTRACTOR here) and the /subcontractors 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.