How to create an email to submit invoices to QBO via email?

Good day, info895.

You can follow these steps to create a template for your invoice and update the email body:

1. Go to the Gear > Custom Form Styles.
2. Click the New style drop-down menu located in the upper right-hand corner.
3. Select Invoice.
4. In the Create invoices that turn heads and open wallets window, click the Emails tab.
5. Enter the message and click Done after. 

Once done, make sure to set the template as default. Please see this sample screenshot for reference:

I've got this article for more details: Customise your invoice emails.

If there's anything else you need, please let me know. I'm just a few clicks away to help you some more. Thanks.