What browser did you try? What happened when you tried to use it?
Chrome. but the browser doesn't matter.
What is broken is when you have added the Act Premium Contact Link to your Office365 tenant and the button appears in users mailboxes (I'm talking about outlook.com, not Outlook installed on a Windows or Mac), the first time you use that button you are prompted to login. The login is broken - you get an error (see below). When contacting ACT for assistance I was told this is because "Premium Contact Link" isn't working on the current release and they don't know when it'll be fixed. This same explanation was given to me from a 3rd party host as well.