If your simbrief alias has strange chars like and underscore it supposedly won’t work. They detailed in an earlier post here that you can create a simbrief.ini file with these lines in it
[simbrief]
username=myweirdsimbriefaliasname
create this in this directory-
C:\Users{USERID}\AppData\Roaming\Microsoft Flight Simulator\packages\microsoft-aircraft-a310-300\work
and it should detect your weird simbrief user alias/name if you have one. In my case my own one is far too long.