This indicates that you have not configured a Captive Portal Rule that allows the users to connect to your guest WiFi. This error is displayed when
You have not created a Captive Portal Rule at all for that location and SSID combination or
You have set your Captive Portal Rule parameters so specifically, that they exclude the users getting this error.
This error page will be displayed the moment the captive browser tries to load your portal on the user’s device.
To resolve this issue, we recommend that you create a base Captive Portal Rule, with minimal restrictions, that will be visible to all users visiting your location.