You can download invoices for all your paid subscriptions in the Billing panel.
Download invoices for PRO users
Instructions
Go to your Account details (click the top-right User Icon > Account details).
Click the Billing option.
Click the Go to Billing Panel button.
Click the option Billing History. Now you can download your previous invoices.
If you haven't paid to upgrade your account, you don't get access to the Billing Panel.
Download invoices for Teams or Enterprises
Instructions
Click the top-left Pages button and scroll to your team.
Click the Team Settings button to open the Team account details.
Click the Billing option.
Click the Go to Billing Panel button.
Click Billing History to download your paid invoices.