Server at 127.0.0.1:3001 (sub domain) is not working, 127.0.0.1:3000 (main) is working fine.

Hello everyone. Currently I am deploying the site to the vps. I successfully ran the nextjs app in home directory(domain.com) in 127.0.0.1:3000 but the PERN stack app in admin.domain.com.au, the frontend is working right, but it seem the server at 127.0.0.1:3001 is not working(I tried netstat -plant | grep 3001 command and it doesn’t show up).

error log:

[error] 56833#56833: *57 connect() failed (111: Connection refused) while connecting to upstream, client: 110.44.115.155, server: admin.domain.com, request: "POST /api/users/login HTTP/1.1", upstream: "http://127.0.0.1:3001/api/users/login", host: "admin.domain.com", referrer: "http://admin.domain.com/login"
2022/10/06 18:05:05 [error] 56833#56833: *65 connect() failed (111: Connection refused) while connecting to upstream, client: 110.44.115.155, server: admin.domain.com, request: "POST /api/users/login HTTP/1.1", upstream: "http://127.0.0.1:3001/api/users/login", host: "admin.domain.com", referrer: "http://admin.domain.com/login"

nginx configure file:

server {
        listen 80;
        listen [::]:80;

         root /var/www/admindomain/frontend/build;

        # Add index.php to the list if you are using PHP
        index index.html index.htm index.nginx-debian.html;

        server_name admin.domain.com www.admin.domain.com;

        location / {
                try_files $uri /index.html;
        }

         location /api {
            proxy_pass http://127.0.0.1:3001;
            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;
        }

}