I'm here to share a few details about entering discounts in QuickBooks Desktop.
Yes, there's a way to apply it. First, you'll have to create a subtotal item first then apply the discount item to it. This way, the discount will be calculated on all line items. Here's how to do it:
Creating a Subtotal Item
1.Click on the List menu, and then select Item List.
2.Select the Item menu and then click New from the pop-up menu.
3.In the Item details , click Subtotal from the drop down list under type.
4.Name the item and then give it an optional description.
5.Click OK to save the item.
For additional reference, you can check this article to learn more about:
Please let me know if you have any questions about QuickBooks invoicing. I'd be happy to help you answer them. Have a good one!