For MetaMod to work properly on your CS:GO gameserver, you need to install SourceMod on the gameserver first.
First you should download the appropriate version of SourceMod, this would be for a Servertux CS:GO gameserver: "Linux".
2. Unpack the archive, after unpacking you should have the following folders/files on your PC: addons, metamod sowie metamod.vdf Files.
3. Connect to our FTP server with your FTP credentials.
4. Now you only have to upload the unzipped files into the folder "csgo".
5. After that you can restart your CS:GO gameserver and check ingame in the console with the command: meta list, if MetaMod was activated. The gameserver should return the following if you have done everything correctly: "No active plugins loaded". Otherwise the gameserver would tell you that it didn't recognize the command.