I’m not sure about C++, but with blueprints all you have to do is to check the Steam Online Subsystem plugin and then edit the .ini file with the information about your Steam ID. You don’t need the appid.txt at all, unless possibly if you don’t have a Steam ID yet. For my VR experience I did not have the appid.txt file. Regarding Steam DLL’s, you may have to add them in a C++ project but for blueprints UE4 will do that for you.