FastX uses the nodejs web server to serve a node js app in the user space. Linux distributions do not by default allow node apps to run on typical Http and Https ports ( port 80 and port 443 respectively) as they are considered privileged ports can can only be run as root.
You can use your firewall to redirect traffic from port 80 to the FastX web server port. For example
sudo iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -j REDIRECT --to-port 3000
Other solutions involve using a web server to proxy the traffic to your FastX server