Within Teamwork Projects, the default email address for the invoice and subscription emails will be your site owner address when you subscribe to a Projects plan.
To change this to any other email address, click your profile image near the top right corner of your site, and choose 'Subscription':
In the Subscription area, under your current plan summary, click the gray 'Update Payment Details' button just below your next payment date.
You will then be able to update the billing email address for invoices going forward in the billing details modal.
For some subscription plans, the steps to update differ. Click the 'View Invoices' button to the top right of your Subscription area to view your invoices.
This will bring you to the invoice history tab:
Scroll to the bottom of the list of payments, where you will see a link to 'choose another email' address:
Note: Only site administrators in the owner company can access this area.
For more information see: Adding more users to your subscription on per-user plans