upstream timed out (110: Connection timed out) while reading response header from upstream nginx in nodejs project

Question

While I had not connected this server to Domain or integrated SSL, it was working fine, as soon as I implemented the SSL it started throwing error.

Here is my server block - sites-available - config.

server{
    server_name demo.example.com;
    location / {
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header Host $host;
        proxy_pass http://127.0.0.1:3002; (I have used just proxy_pass in one config and still had the problem so added this set header)
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade"; (I have tried with just "" but it didnt work)
        proxy_read_timeout 300;
        proxy_connect_timeout 300;
        proxy_send_timeout 300;
        
    }

    listen 443 ssl; # managed by Certbot
    ssl_certificate /etc/letsencrypt/live/demo.example.com/fullchain.pem; # managed by Certbot
    ssl_certificate_key /etc/letsencrypt/live/demo.example.com/privkey.pem; # managed by Certbot
    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot


}
server{
    if ($host = demo.example.com) {
        return 301 https://$host$request_uri;
      } # managed by Certbot


    listen 80;
    server_name demo.example.com;
    return 404; # managed by Certbot


}