Requesters can't view ticket via url included by a trigger

Hi there,

Our Notify requester of comment update trigger includes a placeholder called {{ticket.url_with_protocol}}. In theory, when clicked this should take the requester to a page where they can view their request, right?

When I click on it, it takes me to our Knowledge Base (Zendesk Guide), asking me to log in. I've tested this flow using an email address which is not an agent email address in Zendesk, so why am I being asked to log into Zendesk Guide? Can't the requester simply view their request and reply to it from an external url? If not, what's the purposes of that placeholder then?

I couldn't find anything on that placeholder online, so I'm wondering if it's an out-of-date placeholder.

Any help will be greatly appreciated! :) 

Oliver