After an extensive search of google, unreal docs and Microsoft visual studio compiler errors, I’ve decided to come here in case someone else runs into the error. I am using unreal 5.3.1, and sometimes small changes make big differences. This was not shown in docs and I had to search through the code to find it. So hopefully it saves you some time, and maybe they’ll update the docs.
short story - #include “Online/OnlineSessionNames.h”