Hey Platinum Angel,
We do not provide support for third-party plugins, so if you are running into issues related to the Advanced Sessions plugin, I’d recommend getting in touch with the creator of that plugin for more information.
However, what I can do for you is provide you with a test project that works with Steam and you can take a look at the setup for your own reference. This should give you a good idea of how to set up a system for Creating and Joining sessions through Steam. Make sure to have Steam running while you are attempting to test.
Have a great day