Debug PostgreSQL Connection via Cloudflare Tunnel

I'm experiencing a connection error trying to connect to my on-premises PostgreSQL server through a Cloudflare tunnel. The server isn't behind any firewall or similar security measures, so I'm puzzled as to why this is happening.

- Ideal Skills: understanding of PostgreSQL, Cloudflare, and networking.
- Outcome: I need a professional who can diagnose the problem and provide a solution.