I need an invoice

You can generate an invoice and download it from the Account & Billing tab of your profile. 

• Scroll down to find your Billing History and click Get invoice;
• Fill out the form (or make sure the details provided are correct);
• Click Download Invoice to get the PDF file.

Note that if you put several items in a single order and pay for all of them at once you will not see the Get Invoice button for every subscription from the order in the Billing History table.