Anyone looking to create a zerotier interface into an unprivileged lxc container can simply update the lxc container as follows
Open the config of the container. It is usually located under /etc/pve/lxc
sudo nano /etc/pve/lxc/XXX.conf
and add the line
lxc.mount.entry: /dev/net/tun dev/net/tun none bind,create=file
Reboot the container
run zerotier-cli listnetworks and you should see that the port_error has disappeared
any questions let me know.