The reverse proxy (Nginx Proxy Manager) is containerized/off-host and reaches the app over a non-loopback address, so binding to 127.0.0.1 made play.wowne.ro return 502. Revert the default to bind all interfaces (original behavior). Direct-exposure hardening is a firewall rule + the already-applied X-Forwarded-For rightmost-hop validation, not the bind address. Operators with a same-host proxy can still set HOST=127.0.0.1.
jwinterm