The attachments feature is working on the demo site. The problem you are having is probably that you are trying to upload a file that is not a video or audio file. This feature is meant for audio and video files only and uses a media player to "show" the files. There is an error message that lists the file types that are allowed after you try to upload a file that isn't allowed but that error message goes away when the page refreshes.
While the feature is working as originally intended, I think it needs to be updated to either allow other file types or show better error messages and prompts so people know what the feature is supposed to do.
I'll get to work on fixing that.