I am glad that you ran my code and you see that it works.
The manageusers.pm file should have the "our" declaration
of $LoggedON_user_id and this "our" declaration should not appear anywhere else.
I am not sure what your remaining problem is, but I suspect that the solution will be simple once
the problem is fully understood.
Again, try to make a very, very simple example of the problem. Forget the web server for
the moment. Get your script to work from the command line.
Your "cgi" script doesn't even need to import $LoggedON_user_id as long as it does
"use manageusers ();", (which imports nothing), you can still access $manageusers::LoggedON_user_id as long as manageusers.pm has something like
our $LoggedON_user_id = "default";