If you encounter the error "Can't connect to Skype", like in the picture below, first you need to find out if you are using Classic Skype version (the only Skype version compatible with the plugin), which can be downloaded from this link: http://download.skyprivate.com/skype/win/SkypeSetupFull.exe
If you are already using Classic Skype version, whose interface looks like in the picture below, but you still encounter the error, then in this case you need to give access of the plugin to Skype.
In order to give access of the plugin to Skype, you need to take the following steps:
1. Go to your Skype window and click on Tools-->Options
2. A new window will pop up and you need to click on Advanced
3. After that, click on "Manage other programs' access to Skype"
4. A new window will be shown, which includes all the third-party programs that can have access to your Skype. Go to the SkyPrivate plugin (PayPerMinute.exe) and click Change
5. Make sure you have the option "Allow this program to use Skype" checked, then press Ok and Save
And that is all. After you take these steps, you should be able to log into the plugin.