Send metadata to front-end

I need to send a metadata dictionary to the front-end (Botfront’s webchat) via the websocket channel. I have tried dispatcher.utter_message(text='...', metadata={...}), but it does not work. However, I do not know whether the problem is Rasa is not sending the metadata or the front-end is not interpreting it the right way. So… can I send metadata that way? If not, how can I do it? Thanks!