Why is a product shown in the catalog but unavailable for ordering?

Product availability depends on the specific warehouse (Service Center). If a product is displayed in the catalog but shows «Out of stock» when placing an order, it means the product is not available at the warehouse you selected. Try choosing a different Service Center, or select "Full catalog" in the filters. Also, make sure that the items in your cart share common warehouses — items from different warehouses cannot be combined into one order.