Thanks for joining the Community, @AW95.

I can share some details about adding a mark-up column for your customers' invoices in QuickBooks.

Having the ability to add a mark-up column on your customers' invoices isn't an option in both QuickBooks platforms (Desktop & Online). If you're referring to adding a markup column for estimates, then this is possible in QuickBooks Desktop. You can do this by putting a check mark on the mark-up button on your template. 

Here's how:

1. Click on Customers at the top.
2. Select on Create Estimates.
3. Click on Formatting.
4. Choose Manage Templates.
5. Select Add Customization.
6. Click on Columns.
7. Put a check mark on the Mar-up box.
8. Click on OK to save changes.

Also, our development team is constantly working to improve the product and appreciates the help of users in bringing things like this to their attention.

 I've already taken note of your request and will inform you whenever we have it available for our users. On the other hand, I'd suggest visiting our QuickBooks Online Blog regularly to be updated with our latest news and updates including product improvements. 

Please know that I got you covered should you need anything else with QuickBooks Online. I'd be pleased to help you out. Have a nice day.