...
After your first purchase, you may return to the 'Purchase Plans' page will only display the types of to purchase licences to the subscription plans available and that you will not be able to purchase additional licences in this page. To do so, please click on the link provided (see below) or click 'Subscription Plans', followed by 'Current Plans', then 'Add Licence'.
have not purchased before only.
Otherwise, you will see the 'Manage Your Current Plans' button, which will direct you to the 'Current Plans' page to purchase additional licences by clicking 'Add Licence' instead there.
...
Purchase Additional Licences Subsequently (Add Licences)
...