Bug/Issue "Multiplayer via Steam friends" greyed out

I'm trying to invite a friend to my game via Steam, but his menu has "Multiplayer via Steam friends" greyed out. He does not recieve invites when I try to send them.

Edit: He's reinstallling to see if this fixes the issue. This did not fix it.
Edit 2: For f**ks sake.. All it took was to restart steam.

 

it didnt do anything when i restarted...
do you know what to do?

 

I'm still having this problem and I haven't found a single solution. I've asked for help for weeks and no one has replied to me.

 

I'm having this problem to please help

Edit
The steam restart worked butt you have to exit steam directory hope this helps

P.s also I have already restarted steam many time no idea why it worked this time

 

I'm having the same problem, I've tried restarting steam(multiple times), updating the game, Restarting my pc, and reconnecting to the internet, None of which worked.

 

Both players must be friends on steam, your profiles should be prefferably public and have working steam application.
Otherwise i don't know. It may also come down to the software interfering like chamachi and just the operating system like Mac OS or Linux