Having problems setting up Captive portal on 300m . What is the address for a default splash page?
Are you referring to Web Portal (AP > Wireless SSID > Web Portal Login)? Please take note Web Portal needs to work with InControl2 (to be configure on InControl2) or external Splash page server (so IP address will be public IP of Splash page server).
If AP is managed by Balance router then Captive Portal will be configure there. So IP address will be Balance router LAN inteface IP if you are using built-in Splash page. Else it will be public IP of external Splash page server.