Hello there, @Katy K.

I want to ensure we're on the same page. If you're referring to adding a line in between the items when creating invoices/estimates, you may need to click on the last box/line under Product/Service. But if you mean adding a blank line between 2 already existing lines to add a product or service, it's currently unavailable in QuickBooks Online (QBO).

If you want to personalize your sales forms and add important information that matters to your business, you can do so. QBO has the tool to create attractive, professional-looking invoices, estimates, and sales receipts. For the detailed process, visit this article: Customize invoices, estimates, and sales receipts in QuickBooks Online.

If you need tips and related articles when managing your account in the future, feel free to visit our Community website for more insights.

If you have any more questions or concerns, please don't hesitate to comment below. Have a good rest of your day!