Hello, pbb2.

The email template for payment receipt is a default setup in QuickBooks Online (QBO). You'll have to manually edit its body message before sending it to your customers.

Here’s how.

1. Go to the Plus icon.
2. Select Receive Payments.
3. On the receive payment window, Select the Customer and the Invoice.
4. Click Save and send.
5. Then, update the Body of the email. Click Send and close.

For reference on how to customize templates for sales transactions, you can read through this guide: How to customize invoices, estimates, and sales receipts.

Please let me know if you have other concerns. I'm just around to help.