HTTPS is extra

No domain? Stop. HTTP on the public IP is the demo. http://PUBLIC_IP/health. Skip Certbot.

DNS actually works? Then:

sudo apt install -y certbot python3-certbot-nginx
sudo certbot --nginx -d api.yourdomain.com
curl https://api.yourdomain.com/health

If DNS is lying, Certbot fails. Fix DNS. Don't panic.

curl https://api.…/health can be {ok:true} while POST /auth/register is 500. Health skips the database. Accounts only land in Neon after .env exists on EC2.