reverse proxy websockets

Hi All,

I hope you can help me. I have multiple sites and in front of this i have an nginx revers proxy to handle all the requests. Now with every site that is using websockets its not working for me from my company proxy. if i access my websites elsewhere it works. However if i access another websocket url (from mattermost for example) it works. If i enter my mattermost website again i get a websocket error.

error during websocket handshakeL unexpected response code: 400

How can this be resolved.??