Unable to connect terminal : WebSocket connection failed

I installed mender-connect on my clients and i can see the “launch a new remote terminal session” from mender server dashboard but when i click this link, i get a “connection to remote terminal is forbidden” message.
On the console, i get
WebSocket connection to ‘wss://mender.xxx.com/api/management/v1/deviceconnect/devices/cb9a428d-a029-4a96-a662-6d22a8861430/connect’ failed:

Is there something i missed during setup ?
Thanks

New elements to add : file transfer is only working one way :

  • i can upload files
  • i cannot download files
    Is there something with direction of communication ?