When a visitor tries to connect to the WiFi they may received the following error message:
"Error Opening Page - Hotspot login cannot open the page because it could not establish a secure connection to the server"
This occurs when the connection is attempting to access a domain which has not been added to the whitelist for the Walled Garden.
When a visitor connects to the WiFi, before they log in they are placed into a captive portal, this is so the visitor cannot connect to pages before they have authenticated on to your network. The captive portal restricts the domains the visitor has access to and only allows access to sites which are on the Walled Garden whitelist, this would include access to the Purple splash page servers. The Walled Garden whitelist is managed by the controller which manages the network.
When a splash page loads various domains are accessed in the background and it may be that one of these domains is not on the whitelist and therefore causes this error to occur.
To resolve this you must check the controller to ensure the Walled Garden whitelist is up to date, for more information about how to update the whitelist, please refer to your access point manufacturer, for example, Cisco Meraki or Aruba Networks.