mqtt not publishing data onto the broker when qos set to 2

client.publish("topic", payload,qos=2) not publishing data onto the broker whereas the same is working for qos=0 and 1.I have not defined persistence, it is set to default value.

import paho.mqtt.publish as publish

import paho.mqtt.client as mqtt

from random import *

import time
MQTT_IP='192.168.0.23'
MQTT_PORT=1883
global client
import datetime
def on_connect(client, userdata, flags, rc,qos):

    if rc==0:
        print("MQTT CONNECTION ESTABLISHED")
    print(str(client)+'\n'+str(userdata))
        
def on_message(client, userdata, msg):
    print("Message arrived from "+str(client))
    print(msg.topic+" "+str(msg.payload))

def MQTT_CONNECTION():
    global client
    global MQTT_CLIENT_CONNECTED
    try:
        print("IN mqtt connection")
        client = mqtt.Client()
        client.connect(MQTT_IP,MQTT_PORT)
        client.on_connect = on_connect
        client.on_message = on_message
        MQTT_CLIENT_CONNECTED=True

    except Exception as error:
        print("ERROR IN MQTT CONNECTION",error)
        MQTT_CLIENT_CONNECTED=False
def publish():
    global client
    client.publish("1/MB/EM/3/21/IB",2,qos=2,retain=True)    

if __name__=="__main__":
    MQTT_CONNECTION()
    publish()

I have removed all other functionality, for you all to understand better.

You need to start the MQTT client network loop. This is to handle the multi step handshake for QOS 2 messaging.

The python Paho client has 3 ways to run the loop.

1. You can start the loop on a background thread by calling client.loop_start()
2. You can start the loop on the current thread, which will then block forever with client.loop_forever()
3. You can run the tasks that the loop perform within your own loop by calling client.loop() at regular intervals

Which one you choose depends on what else your code is doing, but I suspect that starting the loop on a background thread is probably the best.