When you first connect online to the servers a unigue passcode is added to account.
When moving game to a new device you will also need to move this file.
It is located in Documents/Sightseer/ServerConfig/Admin.txt
It is also saved on steam cloud.

Open steam library right click on sightseer game and open properties.
Choose updates tab and check cloud is disabled or do so.
Exit Steam.
Copy the Admin.txt file from old machine and replace one on new machine with it.
Start steam and game then enter server.
After which you can enable cloud.

Lonestar_Tasharen