https://your-mono-ip/interfaces_assign.php. You must have a third compatible NIC installed. 1 is for WAN, 2 for LAN, and 3 for the AP. Enable the captive portal on the third interface (OPT1 by default).
If your mono will have only two NICs then you must enable CP on the LAN and use the Pass-through MAC feature (
https://192.168.1.254/services_captiveportal_mac.php) to create your whitelist.
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