Failed to upgrade websocket connection

I am using the production docker from the github page and working in a native android client based off the github version to connect to it.

I am trying to use @GET("api/v3/users/websocket")

but I am getting this error:

Bad Request
{"id":"api.web_socket.connect.upgrade.app_error",
"message":"Failed to upgrade websocket connection",
"detailed_error":"",
"request_id":"4n5kaj8pmbge8nkctcw15zhorc",
"status_code":500,
"is_oauth":false}

What does this mean and how do I fix it?