captive portal not working

Hi,

Please refer below article if that could be helpful

https://community.fortinet.com/t5/FortiGate/Troubleshooting-Tip-Stop-the-captive-portal-triggering-in/ta-p/266583

https://community.fortinet.com/t5/FortiGate/Technical-Tip-Understanding-the-Browser-s-ERR-EMPTY-RESPONSE/ta-p/277481

During the tests especially with mobile phones it's recommended to turn off the Data traffic. Depending on the vendor of the phone, it will quickly identify the WiFi network as not useful and redirect all the traffic through the mobile network. Some limitation may also come from the use of the CNA (Captive Network Assistant), at least for troubleshooting it's easier to use a standard browser in the phone.