systemd service fails to start (code=exited, status=216/GROUP)

[qdlmcfresh]

❯ systemctl --user status akr
× akr.service - akr
     Loaded: loaded (/home/qdl/.config/systemd/user/akr.service; enabled; preset: enabled)
     Active: failed (Result: exit-code) since Mon 2022-12-05 22:44:33 CET; 20s ago
   Duration: 211us
    Process: 66362 ExecStart=/usr/bin/akr start (code=exited, status=216/GROUP)
   Main PID: 66362 (code=exited, status=216/GROUP)
        CPU: 0

Dez 05 22:44:33 arco3 systemd[710]: akr.service: Scheduled restart job, restart counter is at 5.
Dez 05 22:44:33 arco3 systemd[710]: Stopped akr.
Dez 05 22:44:33 arco3 systemd[710]: akr.service: Start request repeated too quickly.
Dez 05 22:44:33 arco3 systemd[710]: akr.service: Failed with result 'exit-code'.
Dez 05 22:44:33 arco3 systemd[710]: Failed to start akr.

As stated on Stackexchange removing the line containing User=username from the service file fixes this.