How to add Mods to your American Truck Simulator Server
Open the Game
Go to the mods manager
Enable the desired mods
Enter Drive
Open the Dev console
Type export_server_packages (Only works while driving)

Open the American Truck Simulator Data folder.
Tends to be here C:\Users\<User>\Documents\American Truck SimulatorLog in to the Kinetic Panel
Stop the server.

Open File Manager.

Navgaite to .local > share > American Truck Simulator
Replace the server_packages.dat & server_packages.sii with your own
Start the server.
