As an admin, you can find the invoices for your Papershift subscription online at any time via your account. Here you can also change the payment data such as billing address, billing email, and payment method.
Click on the gear wheel (Settings) at the bottom left, then on Subscriptions/Addons. Here you will find the following section:
Click ⇾ to the customer dashboard, there you can change your payment details, view the individual subscriptions and download the invoices.
Just click on the individual subscriptions and click on the download icon on the right.