Thanks for posting your concern here in the Community, @gayle12.
For now, printing an invoice with a zero amount will automatically mark it as PAID in the Print window. The system categorizes this type of transaction as paid since your customers don't have to pay it anymore.
However, you can look for a third-party app that will help in accomplishing your task in QuickBooks. All you need to do is go to the Apps menu and search for the app.
I can see how this option would be helpful for you and your business. Therefore, let me take note of this as a suggestion to improve your QuickBooks experience.
Additionally, you can check out our QuickBooks Online year-end checklist. This will guide you in completing your task as you prepare for the new year.
The Community always has your back, so please let me know if you have any other questions. More power to your business and keep safe.