Hi there, Pwoolly.
I understand the urgency of having this feature added asap. We'll wait for the update from our Product Team. For now, you can manually edit the default message before sending it to your customer.
You can check the articles below for additional information about managing invoices and categorising transactions in QBSE:
Don't hesitate to post again if you have other concerns. The Community forum is always open to help you.
