Jo -
It took me a bit to figure this out, there really isn't a "chat stream" like we are normally accustomed to with group chat. When I want to type something into the clan chat, there is a Title and Content section and doesn't allow you to submit unless both have text values. Seems to be a two step process and makes for each message to be a post where everyone can comment, rather than a continuous chat stream.
http://i.imgur.com/4Pw4Uzk.png
Could be confusing at first, but it actually makes sense if each post is intended to be chat thread. Just got to make sure that each thread is labeled properly, like having the Title "group chat" which is arbitrary. Deviates from the traditional group chat UX like in groupme for example.