I understand that using the correct invoice message is vital when projecting a professional and trustworthy image, FSMBOATS.

Let me make it up to you by ensuring you can personalize your email message.

In QuickBooks Online, you can remove the greeting entirely from your email template and customize the subject line and the body content according to your preferences.

Here's how:

1. Go to the Gear icon and then select Accounts and settings.
   
2. Select Sales.
3. Scroll down to locate the Messages section, then click the pencil icon.
   
4. Uncheck the Use greeting box.
5. Edit the Email subject line box.
6. Enter the email message you'd like to add to the invoice.
7. Place a checkmark in the Email me a copy box to receive an email.
8. Add the other info, then scroll down to click Save.
9. After that, click Done.
   

If you want to modify your sales forms, you can browse this article to learn how: Customize Invoices, Estimates, and Sales Receipts.

Additionally, I've added this article that'll help you gently remind customers about invoice due dates to receive the payment on time: Send Reminders Automatically or Manually.

Please let us know if you have additional questions or concerns about managing your sales transactions.  Keep safe!