Site.pro is a great website builder product with rich feature set for an affordable price. The extension within Plesk works great and provides a lot of value to our end customers. The extension also provides functionalities specifically for all size hosting companies around the world.
Thomas Loew, Director Alliances, Plesk International GmbH
The plugin works only for customers but not for users of customers. The user will get error "Permission denied".
Make sure that passive mode in FTP server is enabled. Usually it is disabled by default.
When updating "Limited plans" field in the license the plugin needs to be re-installed.
If plugin throws "Access denied" or "Permission denied" error then check what mode your panel is on. Go to "Tools & Settings" -> "Interface management". If your panel is on "Power user view" mode then switch it to "Service provider view". After that the plugin will work however only for newly created customers. So you will need to remove all users created in Power user view mode and create them anew as Customers in Service provider view.