I do not understand anything about how this works. Is this not a desktop app? After I buy credits, how will I know if the VPN is working for my game or not?
As you can see at http://mudfish.net/download link, Mudfish supports multiple platforms though I'm not sure what you're looking for. If you're interesting to the desktop version of Mudfish, please confirm that How to check the basic functionality works fine in your environment. It's a first thing you should test.