For customers on the Business Plan, the Admin can view and download Invoices on the web application.
To do this, login with the admin credentials and access Account & Settings. On the left menu, you will be able to see 'Billing'.
The Billing page contains a section 'Billing History'. You can click on the 'View Invoices' option and you will get a pop up with the past invoices. From here you can download the invoice in pdf format.
Note : Only Admins of the Business plan will be able to view this option.