Valve recently made a change to how their CS:GO servers operate. To start your CS:GO server, you’ll now need a Gameserver Login Token (GSLT) to be registered with your server.
This may seem cumbersome at first, but is fairly easy to do.
One of the advantages of using GSLTs is that people who add your server to favorites will still be able to find and connect to your server, even if your server's IP address changes. This was something that previously was impossible.
Go to the GSLT creation page
You can create a token for your game servers by going to Valve’s official steam gameserver login token page here:
Create your token
To create a token you’ll need to fill in the two fields at the bottom of the page under “Create a new game server account”.
App ID: Fill in the ID of the game you want to create a token for. In this case, 730 for CS:GO.
Memo: Fill in the name of your new token. Make sure it is something you remember so you know which server this is for. For example, it could be the same as the hostname of your server.
Once you click create, your “Login Token” will appear. Simply copy the string, we’ll need it in the next step.
Setting the token
GSLTs can be registered on your server(s) by using the sv_setsteamaccount command in autoexec.cfg.
You can modify your autoexec.cfg file by clicking the Configuration Files icon in the GamePanel.
Once you have added it to the autoexec.cfg file, save the file.
After saving the file, restart the server.