Login to Penta.
Go to the Administration section of the left navigation.
Head over to the “Subscription” page.
There, you can see a list of your invoices and check if they are already “Paid” or still “Pending”.
Click on the invoices and download them.
If you don't have admin access, you can download the invoices after the fees have been charged in the menu "Transactions". The Invoice is being added automatically as an attachment to the transaction after the fees have been charged.