If you are typing your correct SkyPrivate password and still encounter the message "Wrong username or password" when you try logging into the plugin (as in the picture below), most probably your SkyPrivate username does not match your Skype ID. 

In order to be able to log into the plugin, these two credentials need to be the same and since your Skype ID is unique and can't be modified, you have to change your SkyPrivate username to match your Skype ID.

First, you need to find out your Skype ID. Since you installed the plugin, finding it is very easy. You just need to open the plugin and your Skype ID will be automatically detected from the current Skype you are currently logged into.

After this step, you will need to change your SkyPrivate username. To do that, please go to your SkyPrivate account, and in Settings -> Account, you should find Username. Click Change.

Enter your Skype ID and then click the "Save Changes" Button. Your new SkyPrivate username change request will be approved within 24 hours and you will be notified by email regarding the process. After that, you will be able to log into the plugin with no problems.