But, as I have tried to explain in the subject and in the description (english is even complicated with DeepL),the captive portal is NOT on the WLAN, but on the LAN interface.
If you are referring to an Ethernet LAN connection, unfortunately, our devices do not support this feature. However, as Mike mentioned, you can set up a captive portal with a wireless connection (hotspot). This can achieve similar functionality for user authentication and redirection. Let me know if you need any assistance with the setup.