systemd help

I'm trying to make systemd start my terraria server in a tmux session on boot.
I've been trying for 2 days straight now, I really hope someone can help.

This is what I've tried so far:

[Unit]
Description=Terraria
After=network.target

[Service]
Type=forking
WorkingDirectory=/mnt/usb1/appdata/programmer/terraria
User=argon
Group=argon

ExecStart=/usr/bin/tmux new-session -s terra -d "./TShock.Server -world worlds/God_eftermiddag_.wld"
ExecStop=/usr/bin/tmux send-keys -t terra-%i:0.0 "exit" C-m
ExecStop=/bin/sleep 2

[Install]
WantedBy=multi-user.target

When I save the above and do a systemctl daemon-reload and systemctl start terraria nothing happens.
Running a systemctl status terraria.service gives the following output:

● terraria.service - Terraria
     Loaded: loaded (/etc/systemd/system/terraria.service; disabled; vendor preset: enabled)
     Active: failed (Result: exit-code) since Sun 2022-11-27 10:43:05 CET; 3s ago
    Process: 220085 ExecStart=/usr/bin/tmux new-session -s terra -d ./TShock.Server -world worlds/God_eftermiddag_.wld (code=exited, status=0/SUCCESS)
    Process: 220091 ExecStop=/usr/bin/tmux send-keys -t terra-:0.0 exit C-m (code=exited, status=1/FAILURE)
   Main PID: 220087 (code=exited, status=0/SUCCESS)
        CPU: 64ms

Nov 27 10:43:05 argon systemd[1]: Starting Terraria...
Nov 27 10:43:05 argon systemd[1]: Started Terraria.
Nov 27 10:43:05 argon tmux[220091]: no server running on /tmp/tmux-1000/default
Nov 27 10:43:05 argon systemd[1]: terraria.service: Control process exited, code=exited, status=1/FAILURE
Nov 27 10:43:05 argon systemd[1]: terraria.service: Failed with result 'exit-code'.

I used to run a minecraft (java) server with an almost identical systemd file which works.
So my guess is this is either do to dotnet (since terraria requires dotnet) or bash somehow.

I can send the working minecraft systemd file if it helps anything.

I'm running Raspberry Pi OS Bullseye 64-bit on a Raspberry Pi 4B+ 8GB RAM.

EDIT:
In case someone should ask, yes  - running the following line standing in the working directory works:
tmux new-session -s terra -d "./TShock.Server -world worlds/God_eftermiddag_.wld"