Operates on Purchase Orders. In the Zuper client app this module is labeled "Purchase Order" for most companies, and "Material Order" for companies in the roofing industry — the API and data shape are identical either way. Purchase Orders and Work Orders (Service Orders) share the exact same underlying schema and endpoints; they're distinguished only by the purchase_order_type field (PURCHASE_ORDER here) and the /purchase_orders vs /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. Changing vendor via this endpoint is only allowed for Work Orders (Service Orders) — attempting it on a Purchase Order / Material Order is rejected with 400.