Custom Server Access URL not working

[tong_si_nan_pei]

Server Version#: 1.41.6.9685
Player Version#: 2025.15.0 (1053)

I can access my server with url http://xxxxxx.yyyy.net:7571 (Is a CG-NAT +DDNS port forwarding feature of my ISP) using the browser. But adding this as a custom URL does not allow my clients including app.plex.tv to view my server.

What can I check next?

[tong_si_nan_pei]

It says “securely”. But I already have the setting on “preferred”

[tong_si_nan_pei]

No response, I gave up and resorted to using a cloudflare tunnel.