Hello there, @ian-paintspectio.
Thank you for posting here in the Community. I can help you create a Customer Order No. box on the tax invoice.
In QuickBooks Online, you have the option to configure the templates and add a custom field. You can go to the Custom form styles section and edit the tax invoice template.
Here's how:
- Click the Gear icon in the upper-right corner.
- Select Custom form styles.
- Search for the template.
- Press Edit below the Action column.
- Go to the Content tab.
- Click the pencil icon in the upper-right.
- Scroll down and select +Custom field.
- Add an extra field.
- Hit Done.
For additional reference, I've attached some articles you can use to customise the info on your forms, as well as importing invoice templates in QuickBooks:
I'm only a few clicks away if you have any other questions. Wishing you and your business continued success.