Server won't work? Am I doing something wrong?

Hello! I’m trying to set up a gmod server for my friends (and enemies) to connect to, but unfortunately, even when following guides and everything, it doesn’t seem to work.

I have these ports forwarded:

1200 - 1200 UDP and TCP
27000 - 28000 UDP and TCP

and of course sv_lan is set to 0 and I tried heartbeat.

Did I miss something in the guide? Did I do something wrong?

Any help is greatly appreciated.