Captive Portal - Configuration issues

[PotatoCarl]

Hi
I am trying (once again) to get the Captive Portal with my Guest network to operate. However, the problem is, that the client is not automatically forwarded to the login page.

I configured it according to the documentation (https://docs.opnsense.org/manual/how-tos/guestnet.html).
I can see well the login page when I address ist manually like 192.168.100.1:8000
However, otherwise I just get "server not found" when I try to open any page, no matter if https or http

Not sure what is going wrong. When I select the IP as "no authentification needed" it also works fine, so the portal somehow works, but the captive page is not displayed.

Any suggestions? Thank you.