WiFi Access with Disclaimer Page

We have recently purchased a FortiGate 300C and I am working on setting up public wifi access on it. I would like for guests to only go to a disclaimer page and not have to enter credentials to gain access. I have configured a SSID using Captive Portal security mode. I' ve created a guest user and added it to a guest user group. On the SSID, I' ve selected the appropriate user group. On the Policy setting, I created a Firewall policy of subtype Address and checked the Disclaimer option. When joining the Public WiFi, users are still being prompted to enter a user name and password. Need some guidance on the best way to set this up. Thanks!