The ability to customize the email address used for sending invoices using Gmail is only available through the QuickBooks Online web browser interface, Daniel. 

We value your feedback and would like to submit your suggestion to our product engineering team. Your input could be key in developing a feature that enhances the invoicing process for you and other users.

To share your feedback, please follow these steps: 
 

1. Click on the Gear icon located in the upper right corner.
2. Select Feedback under the Your Company section. 
   
    

   

3. In the feedback form, enter your comments regarding the customization of the email address feature. 
4. Finally, click Next to submit your feedback to our team.

Also, when you need to make changes or update your invoice payment, you can do so through the QBO app. Please visit this article for detailed guidance: Edit an invoice payment using the QuickBooks Online app.

If you require assistance, please do not hesitate to visit the Community. We look forward to providing you with support once again.