Billings
Log in to my.quentn.com. Do not click on your system, but click on My Account and Billing / Subscriptions in the upper right corner.
Under My invoices you will find them listed and you can download them.
Get your invoices sent automatically
If you want your invoice to be sent automatically, go to my.quentn.com and click on "My Account" and "Account Settings". Here you can check the box to have the invoice sent to the email address you registered your Quentn account to.
An extra email address for the invoices cannot be stored.