Laravel Spark + Echo + Pusher unable to assign socket

I have set up Pusher on Spark and I can create an event which shows up on the Pusher debug console, but it has not assigned a socket and the client can not listen for it.

.env:

QUEUE_CONNECTION=sync
QUEUE_DRIVER=redis
BROADCAST_DRIVER=pusher

'default' => env('BROADCAST_DRIVER', 'null'),

window.Echo.channel('messages').listen('.newMessage', ({task}) => {
                this.tasks.push(task.body)
            })

 public function broadcastAs() {
        return 'newMessage';
    }

    public function broadcastOn() {
        return new Channel('messages');
    }

require('spark-bootstrap');

import Echo from 'laravel-echo'

window.Pusher = require('pusher-js');

window.Echo = new Echo({
    broadcaster: 'pusher',
    key: process.env.MIX_PUSHER_APP_KEY,
    cluster: process.env.MIX_PUSHER_APP_CLUSTER,
    encrypted: true
});

require('./components/bootstrap');