You can retrieve your invoices by following these steps:
Login in to your account
Click on "Account" in the top right corner of the page
Click on "Orders"
On each order, click on "Details"
Click on the "Print" icon in the top right corner
Your "bid won" email also serves as an invoice.
If you have any questions about how the "bid won" email serves as the invoice, please email firstname.lastname@example.org.