By default all administrators of your organization will receive each invoice by email. All previous invoices are also available in the "Billing" menu.
Sending invoices to additional recipient
- Go to the "Billing" menu
- Click on "Manage additional invoice recipients"
- Add that (or these) person's email
- Save
All future invoices will be sent to these people as well. You can also "see all" previous invoices right below that button.