Hi cmi5,

Thanks for your update. You'll have to check the Default email message on your sales forms under the Company settings of your QuickBooks Online account. Here's how:

1. Click on the Gear Icon.
2. Click on Account & Settings.
3. Click on Sales tab.
4. Look for Messages field and under Email message you can edit the default email sent to your customers.
5. Make your corrections, and click on Save and Done.

The email message attached to your invoices will be updated moving forward.

If on the event you need to make changes for an individual customer you will have to manually edit the message during the invoice creation page. You can check this article for your reference: How to set up or change customer messages.

As always you're welcome to post again here if you have questions.