Could you possibly add mudfish support for Steam itself? The software, not just the website? As to why, well some games specifically Nexon games had their IP block lifted when Nexon EU was shut down, however that IP block was never lifted from Steam itself, out of laziness I suppose… I believe other games suffer from IP block as well, and it would be nice to have support for Steam on mudfish, so it is not necessary to login via Full VPN.
I could still make a package dump when logging into steam for you but I have many things running, I’m not sure if it’s going to help. Nevertheless the IP check is performed when you log into steam.
Please confirm that How to check the basic functionality works fine in your environment. It’s a first thing you should test.