Connection to Homeassistant MQTT Broker refused

I've setup an mosquitto mqtt broker on my homeassist. I now want to have my esp32 connect to it and afterwards control a lamp over BLE.

I'm currently already stuck trying to connect to my homeassistant mqtt broker. I've validated the broker is working with mqtt.fx by subscribing to the same ip/topic with the same credentials. When I now try to subscribe to the same broker I always get the following error:

Connection refused, unknown return code: NaN.

This is how my code looks like:

var wifi = require('Wifi');

var ssid = 'ssidname';
var password = 'mypassword';
var port = 80;

var mqttServer = "192.168.86.42";
var mqttConfig = {
    client_id : getSerial(),
    username: "mqtt-user",
    password: "my-mqtt-password",
    keep_alive: 60,
    port: 1883,
};

var topic = "/lrcontroller/";
var message = "hello, world";

var mqtt = require("MQTT").create(mqttServer, mqttConfig /*optional*/);

function mqttConnect() {

  console.log("connecting mqtt");

  mqtt.on('error', (error) => {
    console.log("mqtt error: "+error);
  });

  mqtt.on('connected', function() {
    console.log("MQTT connected");
    setTimeout(function() {
      mqtt.subscribe(topic+"#");
    }, 1000);
  });

  mqtt.on('disconnected', function() {
    console.log("MQTT disconnected... reconnecting.");
    setTimeout(function() {
      mqtt.connect();
    }, 1000);
  });

  mqtt.on('publish', function (pub) {
    console.log("topic: "+pub.topic);
    console.log("message: "+pub.message);
  });

  mqtt.connect();

}

wifi.connect(ssid, {password: password}, function(error) {
  if(error){
    console.log("wifi errors: "+error);
  }
});

wifi.on('connected', (info) => {
  console.log("wifi connected to " + info.gw + " with the ip: " + info.ip + "! ");
  mqttConnect();
});

wifi.on('disconnected', (error) => {
  console.log("wifi disconnected!");
  setTimeout(() => {
    console.log("wifi reconnecting ...");
    wifi.connect(ssid, {password: password}, function(error) {
      if(error){
        console.log("wifi errors: "+error);
      }
    });
  }, 1000);
});

I am wondering if I am missing something here?

Also when I flash to my esp32 with the Espruino IDE, the console logs are not shown because wifi seems to still be connected after te restart. So to validate my code I always call wifi.disconnect();.

Would really appreciate any help!