If you're looking for an old invoice, we can show you where to go.
If you're the Admin on the account these will be sent to you automatically on the renewal date. If you need to find these manually, simply go to:
Configure > Plan and Billing > Billing history
How can I add a third party invoice receiver?
Go to Configure > Settings > Email Notifications > Send a copy of all invoices to:
(Please note: This is only available for active accounts that pay via credit/debit card)