FortiGate 40F running v6.x

[Martinjoe]

Hey everyone,

New to Fortinet firewalls! I'm setting up a FortiGate 40F running v6.x with a custom payment gateway (xyz com). Here's the issue: after reaching xyz com, I can't log in. The screen goes completely white and the browser keeps loading forever.

Any ideas why this might be happening and how to fix it? I have seem some website doing greatly, like phozellpay.com authorize etc

Thanks!

[johnathan]

The problem isn't very clear, just wanna confirm that you are using that site as a captive portal but it never loads for the end user? 
There may be additional  domains needed for that page to load properly, you probably can't allow just 'xyz com'.
The easiest way to see this is by pressing F12 in the browser, navigate to the 'Network' tab, refresh the page, and see what requests are failing.