few issues for debian

[lennoknet]

few thing to consider if you use debian - better install sudo and add your user to sudoers
otherwise go into user root by
su -
and ignore all the sudo

firewall ufw will be enabled!
add ssh to it in case you connect via ssh

either use
sudo ufw disable
or
sudo ufw allow 22/tcp

missing dependencies
sudo apt install libatomic1 libasound2 libpulse0

service file changes needed:
exchange +login anonymous with +force_install_dir commands, the order is wrong
vein_server.sh missing the port parameters so default will be used no matter whats in your game.ini

so change lines as follow by
sudo nano /etc/systemd/system/vein-server.service

ExecStartPre=/home/steam/Steam/steamcmd.sh +force_install_dir /home/steam/Steam/vein-server +login anonymous +app_update 2131400 validate +quit
ExecStart=/home/steam/Steam/vein-server/VeinServer.sh -QueryPort=27078 -Port=27077

then reload daemons
sudo systemctl daemon-reload

the dashboard has hardcoded port and should be selectable, if you dont like the port edit script accordingly before running it.... also python dependencies missing. since i dont need dashboard, maybe reopen first issue and investigate