Because of some upcoming changes in our platform, Plesk had to be removed from the customer marketplace.
You can still order Plesk subscriptions using the reseller control panel.
This article explains how to do this.
Go to 'Classic panel' on reseller level
Click 'Billing' to go to billing
Click ‘Orders' > 'Add new order’
Now Select the ‘Account' , ‘Service plan’ (Search for 'Plesk') and 'Subscription Period’
Click 'Next' a couple of times and confirm the order.
Now Plesk will come available on the customer portal.