Node JS hosting using Nginx Reverse proxy gives 404 error

Question

I want to host a Nodejs API server to my digitalocean server where a WordPress application is already running using Nginx and PHP fpm

I followed the below link to set up the WordPress application and it's working fine now. https://www.digitalocean.com/community/tutorials/how-to-configure-nginx-as-a-web-server-and-reverse-proxy-for-apache-on-one-ubuntu-18-04-server

I wanted to set up Nodejs application inside the same server for demo purposes and I followed the digitalocean guide for setting up node js with a different config file and subdomain.

https://www.digitalocean.com/community/tutorials/how-to-set-up-a-node-js-application-for-production-on-ubuntu-16-04

My Nginx config for node application looks like this

server {
server_name sub.domain.com
location / {
    proxy_pass http://localhost:6969;
    proxy_http_version 1.1;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection 'upgrade';
    proxy_set_header Host $host;
    proxy_cache_bypass $http_upgrade;
}

}

I have allowed port 6969 using ufw allow 6969.

I am able to access the Nodejs application using sub.domain.com:6969 but sub.domain.com gives me a 404 error. (404 Not Found nginx/1.18.0 (Ubuntu))

I want to access Nodejs application directly without a port number. I have checked Nginx logs and there are no errors, and configures is gives success in nginx -t

Please give me some suggestions to debug and fix this issue. I don't have much knowledge in Nginx configuration. I was just following tutorials from Digitalocean to configure the WordPress and node application.

Thanks in Advance