My server only works on localhost but not works on ip address.

Hello, I’m using ubuntu 20.04 droplet. I’ve seen many tutorials that talked me that I don’t need many things to see my app run on the internet. They said that just run “pm2 start app_name” and then I can see my website on the internet by send my browser to “server_ip_address(ipv4):port_number”. In video, that works. But not for me.

When I try “curl http://localhost:port_number” or “curl http://127.0.0.1:port_number” in server connected bash, it works. But when I try to connect by ip address outside of server computer(or bash) the browser load page endlessly. I can’t get any logs both in digitalocean graph and pm2, about my attempt using ip address.

It happens even before I install nginx to server. I’ve heard that after install nginx, i can default nginx html when I get to my server ip address, but that also does not work.

Why does this happens? I can’t get where does this problem comes from. Because I use ipv6? Or because I set firewall which is in doc “Recommended Initial Droplet Configuration” (https://www.digitalocean.com/docs/droplets/tutorials/recommended-setup/)? And how can I solve that?

“netstat -plant | grep port_number” gives me this. tcp6 0 0 :::port_number :::* LISTEN PID/node