Linux Networking

Using port 443 (Privileged)

Running service as root

By not giving user to .service file application should run automaticaly a root.

Lower privileged port trheshold

If you application can't run on 443 it's because you have to run in in root. One of the move aways is to lower ports range, try:

sudo sysctl -w net.ipv4.ip_unprivileged_port_start=443