Hello my dear hope, 
After I bought the game a few days ago and I wanted to join a server full of anticipation, after a few seconds it comes out again and again into the main menu, with this error message
“Game joining failed (joining the game you requested failed)” 
In the single player co-op I can play it too 2nd
AntiVir off already
Firewall also off
Reinstall tried
Is it Battleeye?
I’m really baffled and really do not know what to do … (
Can you help me please ???
Best regards
Can you give us some more informations ?
For example: you have this message if you try to join ALL servers ?
It was a private server or an official server ? What type of game (PVE, PVE-C or PVP) ?
Are you sure you wasn’t trying to join a server with mods or another version of the game on ? (have you enabled automatic updates on steam for the game ?)
Because to understand what’s happening we need to know, it’s an error I never had. 
Hello!!
Yes any server, whether PVE, PVE-C or PVP or private or official server …
Have the current version that I have also set this on Steam so I always have the latest version.
At the same time my buddy has the game installed as well and can join every server.
I can only play with him in Coop mode and this without any problems.
Also I can not join server on Battleye and have no Battleye where.
Unfortunately, I have no idea what the problem is 
Can it be battleye?
If you don’t have Battleye installed I think you cannot join official servers.
Anyway you can use filters, from the page where you search a server, to see only servers requiring battleye or without it.
But if the problem occours with ALL existing servers you tryed the first responce in my mind is maybe you have a firewall installed on your PC or your LAN and you have to set it to allow ConanExiles etablish connections.