How can we combine the non-inventory and the inventory items in one invoice? | SAP-SD

To combine the inventory and the non-inventory items in one invoice, change the non-inventory items to deliverable but not pick able. Apart from this, change the copy rule for orders-> invoices and deliveries->invoices to permit invoice combination. However, to create combined invoices, the PO number, payment terms, Sales organization, and distribution channel must be identical; otherwise, undesirable invoice combination may be created.