Hotspot POD Login Page Custom Port

Hi There,

we have a Guest WiFi with Hotspot Mode enabled.
Today we have Guests with personal Firewalls on their Laptops which only allows 80/443 TCP outgoing (in addition to non-web like DNS etc.).
The Guests have no access to the configuration of their personal Firewalls and cannot disable.

How can i change the default Port 4501 of the Sophos UTM POD login page to something else?
my login-page is HTTP only so why can't i use Port 80?
Port 80 on the WiFi Interface of the UTM is free, so why can't i use it?

regards,

Daniel