Hi there, @JackAle.

Allow me to chime in and share some insights on how to show added customer messages when printing in QuickBooks Online (QBO).

We'll need to add a custom message directly to the invoice to show it on the print preview page. I've included a screen for visual reference.

Lastly, I've got you these helpful articles you can read for ideas about how you can manage your customers and sales transactions: Income and Expenses for QuickBooks Online.

If there's anything else that I can help you with, let me know in the comments. I'll be happy to help.