Since Woocommerce mega major Update 3.0+ things have changed quite a lot: WC_Order properties can’t be access directly as before and will throw some errors. New WC_Order and WC_Abstract_Order getters and setters methods are now needed. There is some New classes for Order items: WC_Order_Item class. WC_Order_Item_Product class. Also see: Get Order items and WC_Order_Item_Product in Woocommerce 3 So also the Order