Valve now requires certain game servers to register a server with a specific Steam account. They acomplish this with a feature called Game Server Login Token or GSLT. This token will uniquely register your server with your Steam account.
Creating a GSLT
First you simply need to head over to the following link and login to your steam account: https://steamcommunity.com/dev/managegameservers
Next you'll need to identify the unique Steam App ID relevant to your server. For Nodecraft customers you can find this ID on the Steam Auth Token tab in NodePanel. You can also reference the table below.
Once you have generated the token you only need to paste it's value into the form on the Steam Auth Token tab in NodePanel.
|Counter Strike: Source||240|
|Counter Strike: Global Offensive||730|
|Team Fortress 2||440|
|Left 4 Dead 2||550|
|Don't Starve Together||322330|
Left 4 Dead & Counter Strike (original release) do not require a GSLT