Hello,
It looks like you’re working on 4.11, which is quite an old version of the editor. Since then, there have been many bugfixes and code changes that could have resolved your issue, and if you’re attempting to follow a guide somewhere, it may have been updated past 4.11 and thus have become incompatible with your engine version.
I recommend upgrading a copy of your project to a later engine version, such as 4.15, and then running through the Steam setup in the guide linked below:
Using the above wiki, I have been able to get Steam set up and running several times using 4.13, 4.14, and 4.15.
Have a great day