Excellent news. Don’t forget to mark as solved.
@sam_nazarko OP was following Running scripts on startup and shutdown and it contains an error: systemd Type = single should be changed to Type = simple .
One example also contains EnvironmentFile=-/etc/sysconfig/network but the description refers to Enviroment (NB spelling).
But nice guide.
Edit: It seems like the guide is suggesting that the .service file should be created in /etc/systemd/system whereas the best location is /lib/systemd/system. That way systemctl enable/disable will create/remove a symbolic link in /etc/systemd/system back to the real file.