Why does Nginx only respond on Port 80?

I tried to change nginx' port 80 to 81 in nginx.conf file but my sample site is not responding despite listening to port 81. The sample website only responds on port 80. Also , sample site on http://localhost:81 is responding. But http://samplesite.com/ is not responding when Nginx is running on 81 Port.I am newbie so I'm having a hard time figuring out the best way to do this. Can somebody tell me how I can run Nginx server on a different port than 80 like 81?

Nginx.conf file:

server {
    listen 81;
    listen [::]:81;

    root /var/www/samplesite.com;

    index index.html index.htm index.nginx-debian.html;

    server_name samplesite.com www.samplesite.com;

    location / {
        try_files $uri $uri/ =404;
    }

}

Not: ufw is inactive