Publish message to Meshtastic chat through MQTT using Java

Question

I'm trying to play around with Paho MQTT for Java to send and listen to messages from my Meshtastic chat. Following an example code and a documentation I found, I tried the following:

import org.eclipse.paho.client.mqttv3.IMqttDeliveryToken;
import org.eclipse.paho.client.mqttv3.MqttCallback;
import org.eclipse.paho.client.mqttv3.MqttClient;
import org.eclipse.paho.client.mqttv3.MqttConnectOptions;
import org.eclipse.paho.client.mqttv3.MqttException;
import org.eclipse.paho.client.mqttv3.MqttMessage;

public class Main {

    public static void main(String[] args) {
        String broker = "tcp://BROKERLINK:1883";
        String clientId = "clientId";
        String topic = "msh/EU_433/2/e/CHANNEL/1234";
        int subQos = 1;
        int pubQos = 1;
        String msg = "Hello MQTT";

        try {
            MqttClient client = new MqttClient(broker, clientId);
            MqttConnectOptions options = new MqttConnectOptions();
            options.setUserName(clientId);
            options.setPassword("PASSWORD".toCharArray());
            options.setCleanSession(true);
            client.connect(options);

            if (client.isConnected()) {
                client.setCallback(new MqttCallback() {
                    public void messageArrived(String topic, MqttMessage message) throws Exception {
                        System.out.println("topic: " + topic);
                        System.out.println("qos: " + message.getQos());
                        System.out.println("message content: " + new String(message.getPayload()));
                    }

                    public void connectionLost(Throwable cause) {
                        System.out.println("connectionLost: " + cause.getMessage());
                    }

                    public void deliveryComplete(IMqttDeliveryToken token) {
                        System.out.println("deliveryComplete: " + token.isComplete());
                    }
                });

                client.subscribe(topic, subQos);

                MqttMessage message = new MqttMessage(msg.getBytes());
                message.setQos(pubQos);
                client.publish(topic, message);
            }

            client.disconnect();
            client.close();

        } catch (MqttException e) {
            e.printStackTrace();
        }
    }
}

Whenever I send a message from my phone I can see it using MQTT Explorer. The message I send from the Java code can also be seen there under 1234, yet it does not appear in the Meshtastic chat. What am I doing wrong?