Nginx, not port 4000

Express on :4000 is for localhost. People on the internet hit 80. Nginx forwards to 127.0.0.1:4000.

sudo apt install nginx -y
curl http://127.0.0.1:4000/health

That curl should already work. Then:

Swipe to pan

Write the server block into a file first. ln only makes a shortcut. If the file is missing, nginx -t fails. Create, then link.

sudo nano /etc/nginx/sites-available/club-api

server_name _; matches anything — including the public IP. That's how you go live without a domain.

server {
    listen 80;
    server_name _;

    location / {
        proxy_pass http://127.0.0.1:4000;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
    }
}

Ctrl+O, Enter, Ctrl+X. If a broken symlink already exists, delete it first:

sudo rm -f /etc/nginx/sites-enabled/club-api
sudo ln -s /etc/nginx/sites-available/club-api /etc/nginx/sites-enabled/
sudo rm -f /etc/nginx/sites-enabled/default
sudo nginx -t && sudo systemctl reload nginx
curl http://127.0.0.1/health

That's on the box. From your laptop (SG must allow port 80):

curl http://PASTE_PUBLIC_IPV4/health

Open it in a browser. { ok: true } and Nginx works. That is not a user in Neon. Hit register on this URL. 500 = no .env on the box. Copy DATABASE_URL onto EC2, pm2 restart, then register again.