Hello there, garrison.

The option to remove the Message on invoice field isn't available. This field helps you enter a note for your customers. However, if you didn't enter any on this box, it will not show on your customer's end.

As a workaround, you can import your invoice template without the Message on invoice field.

I've added this article for more information of the process: Import custom form styles for invoices or estimates.

Feel free to reach us back by clicking the Reply button if you need help in importing a template. Have a good one!