Customer portal is a tool that is useful for end customers if they want to get a better insight into the status of the device that are connected to the network. As they can see which devices are connected, how many data they've used, and how long they've been connected.

It is also used for whitelisting devices that need to bypass a captive portal, since they don't have a built in browser (Smart TVs, Roku, Routers, etc.).

Administrators can find their customer portal link in Settings->Username/password Login->Customer Portal

Users don't need to be on the Guest network to access the customer portal. It is accessible from anywhere, as long as you have the portal's URL.

To log into customer portal, users simply need to log in using the same credentials provided to them for accessing the WiFi network.

To bypass a captive portal, you'd need to find a MAC address of the device that you intend to bypass a captive portal with.

After that, simply go to Connected Devices section, and select Add Device option.