enable changelevel2 in server

hello, i am running the HL2 campaign on my server but i have encountered a problem, the map doesnt change.
it prints

Can't changelevel2, not in a single-player map

i appreciate whatever help you can provide.

changelevel2 only works on single player for the gmod client.
You could make a request for such feature to be extended to listen/dedicated servers - https://github.com/Facepunch/garrysmod-requests/issues