I need an invoice

You can download your invoice from the «Billing history» tab of your profile settings. Just find your subscription and click the «Get invoice» icon;

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» icon for every subscription from the order in the Billing History table.

If you purchase the subscription in the Android or iOS app, you'll get a receipt email from Google Play or App Store.