PubSubClient.h callback() function is not executed

Question

I'm working on ESP32 Arduino IDE. I'm trying to get the message from my MQTT broker using PubSubClient.h and it seems like the callback() function is not working. But when I tried to publish the topic in the Arduino IDE it received the messages from the broker fine. Here is the code:

#include <WiFi.h>
#include <PubSubClient.h>
 
const char* ssid = "XXXX";
const char* password = "XXXX";
const char* mqttServer = "XXXX";
const int mqttPort = 1883;
const char* mqttUser = "";
const char* mqttPassword = "";
 
WiFiClient espClient;
PubSubClient client(espClient);
 
void callback(char* topic, byte* payload, unsigned int length) {
 
  Serial.print("Message arrived in topic: ");
  Serial.println(topic);
 
  Serial.print("Message:");
  for (int i = 0; i < length; i++) {
    Serial.print((char)payload[i]);
  }
 
  Serial.println();
  Serial.println("-----------------------");
}
 
void setup() {
 
  Serial.begin(115200);
 
  WiFi.begin(ssid, password);
 
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.println("Connecting to WiFi..");
  }
  Serial.println("Connected to the WiFi network");
 
  client.setServer(mqttServer, mqttPort);
  client.setCallback(callback);
 
  while (!client.connected()) {
    Serial.println("Connecting to MQTT...");
 
    if (client.connect("ESP32Client", mqttUser, mqttPassword )) {
      Serial.println("connected " + String(client.state()));
    } 
    
    else {
      Serial.print("failed with state ");
      Serial.print(client.state());
      delay(2000);
    }
  }
  client.subscribe("XXXX");
}
 
void loop() {
  client.loop();
  delay(500);
}

The problem is I want to get every messages from my broker. Thank you in adavance.