WSS error: Connection to https://... was not upgraded to websocket

[web75018]

Hi there,
Thanks for the package.

How can is add ssl support?
final String url = 'wss://{my_domain_name_.com}:443/'; => ???
var socket = await Socket.connect(url, listener: new MyListener());
socket.on('rand', (name, data, ack) {
print('got message $data from event $name');
ack(name, 'No error', 'Hi there buddy');
})

Im getting this error:
E/flutter (10461): [ERROR:flutter/lib/ui/ui_dart_state.cc(209)] Unhandled Exception: WebSocketException: Connection to 'https://{my_domain_name_.com}/#' was not upgraded to websocket
E/flutter (10461): #0 _WebSocketImpl.connect (dart:_http/websocket_impl.dart:1017:41)
E/flutter (10461): #1 WebSocket.connect (dart:_http/websocket.dart:379:22)
E/flutter (10461): #2 IoSocketPlatform.webSocket (package:socketcluster_client/src/socket_platform_io.dart:10:51)
E/flutter (10461): #3 Socket.connect (package:socketcluster_client/src/socket.dart:48:47)
E/flutter (10461): #4 main (package:socketcluster/main.dart:39:29)
E/flutter (10461): #5 _runMainZoned.. (dart:ui/hooks.dart:145:25)
E/flutter (10461): #6 _rootRun (dart:async/zone.dart:1428:13)
E/flutter (10461): #7 _CustomZone.run (dart:async/zone.dart:1328:19)
E/flutter (10461): #8 _runZoned (dart:async/zone.dart:1863:10)
E/flutter (10461): #9 runZonedGuarded (dart:async/zone.dart:1851:12)
E/flutter (10461): #10 _runMainZoned. (dart:ui/hooks.dart:141:5)
E/flutter (10461): #11 _delayEntrypointInvocation. (dart:isolate-patch/isolate_patch.dart:283:19)
E/flutter (10461): #12 _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:184:12)

NGINX config:
server{
server_name sub.domain.com;

location / {
    proxy_pass http://localhost:3000; #Nodejs server.
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";
        proxy_set_header HOST $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
        proxy_pass_request_headers on;
    #proxy_http_version 1.1;
    #proxy_set_header Upgrade $http_upgrade;
    #proxy_set_header Connection 'upgrade';
    #proxy_set_header Host $host;
    #proxy_cache_bypass $http_upgrade;
}

listen 443 ssl; # managed by Certbot
ssl_certificate /etc/letsencrypt/live/sub.domain.com/fullchain.pem; # managed by Certbot
ssl_certificate_key /etc/letsencrypt/live/sub.domain.com/privkey.pem; # managed by Certbot
include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot

}
server{
if ($host = sub.domain.com) {
return 301 https://$host$request_uri;
} # managed by Certbot

server_name sub.domain.com;
listen 80;
return 404; # managed by Certbot
}