Don’t use caddy start if you’re also using systemd. Those are two separate ways of running Caddy, and aren’t compatible. If you use caddy start, then it starts Caddy as a background process. Then when you try to start the systemd service, it can’t run because there’s already another instance of Caddy running.
Run caddy stop once for now, then never run caddy start again. Then, run sudo systemctl start caddy to make sure it’s running as a systemd service. Follow these instructions for information on how to use it past that point:
Also, don’t use systemctl status caddy to read your logs, because that command will truncate your logs (notice the > at the end of some log lines). Instead, use the command mentioned in the docs above 