You cannot provide links directly to chat, as they won't work. You have to enter chat through one of the two methods provided -- the "Lobby" link, or the "No popup chat" link listed in the top grayish menu (where it says "Chat").

Unintuitively, if you click on the actual menu item that says "Chat (4)" (or whatever that number is), it probably won't work. You have to go to the dropdown and choose "Lobby" or "No pop-up chat" in order to enter.

We're shutting down the old chat system soon, so we're not fixing any issues that arise over it at this time.

Thanks,
DocJohn