To have automatic redirection for Zero-IT via WLAN you can use BYOD onboarding portal.
Onboarding portal is configured via Guest Access --> Enable the check box next to Onboarding Portal to enable Zero-IT device registration from the Guest Portal.
And change association at WLAN/SSID from policy define at Hotspot to Guest Access Service.
But since it used Onboarding, when user get 1st time to be provision, it will go to onboarding portal 1st
And click on register device. the subsequent screen will have the same screen with WLAN Connection Activation page.