Here, I noted down my exploration in case you want to create only single invoice for each delivery order you made. By doing this setting thus you will guarantee that an individual billing document is created for each delivery. To be able to achieve this, again, you have to consider routine to handle this.
By executed t-code VTFL, or by using path: IMG > Sales and Distribution > Billing > Billing Documents > Maintain Copying Control for Billing Document > Copying control: Delivery document to billing document, enter the source delivery document and target billing document. Furthermore choose the item details, means you choose the item category. On item details overview as shown in screenshot below, in the Data VBRK/VBRP field, enter the routine 3 (individual invoice).