Hi there, @kamjohn.
Thanks for reaching out to the Community. I'm here to provide some information about adding lines between services on your Invoices.
Are you referring to adding lines in between the Product/Services on your Invoices? If so, this option is currently unavailable in QuickBooks Online. However, you can check out for a third party application that supports this feature.
While the option isn't available, I'd encourage you to send us feedback on how we can help you run your business easier. You can do this by clicking on the Gear icon and select on Send Feedback Online. This will be sent to the Product Development Team for review when determining features to be added in future updates.
Please know that the Community is always here when you need it. Have a great day!