When logged in, go to the My Orders section. This can be found in your account menu found in top right menu or on your main account page.
Each order line has a Send Invoice button.
For any order that has a Shipped status, you can retrieve your invoice.
Click Send Invoice and your invoice will be emailed to you.
For more details on this topic watch the below video:
Please note, invoices for orders that contain fixtures, graphics and samples will not be available online, you will need to contact Customer Service, here.