Yes, it is possible, Conor7. We can enter the second email in the designated field and separate them by comma.
Here's how:
- Go to the Customer and Leads menu and click the Customer tab.
- Select the customer you want to add another email address.
- Click the Edit button to make changes.
- Enter the second email and separate them by comma.
- Click Save to finish.

Manage your customer information in QuickBooks to keep your records current and accurate.
Once your customers have paid their invoices, visit this article to record their payments: Record invoice payments in QuickBooks Online.
Whenever you need additional assistance managing your customer information, please don't hesitate to notify us.