[Python] Modbus TCP with Python

I am trying to communicate with Modbus via TCP. I want to use this type of code without a library.

The code is run like this :

sudo python3 modbus_master.py


When I run the program with this code then I see my Modbus connection defined in Wireshark. I am also using slave Modbus programs (more than one) but there is no connection with my master.

What am I doing wrong in the following code?

#!/usr/bin/python3
# This is client.py file

import socket
import struct
import time

# Create a TCP/IP socket
TCP_IP = '192.168.0.107'
TCP_PORT = 502
BUFFER_SIZE = 39
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((TCP_IP, TCP_PORT))

try:

unitId = 16
functionCode = 5
print("\n,Switching plug on")
coilId = 1
req = struct.pack('12B', 0x00, 0x00, 0x00, 0x00, 0x00, 0x06, int(unitId), int(functionCode), 0x00, int(coilId),
0xff,
0x00)
sock.send(req)
print("TX: (%s)" % req)


time.sleep(2)

finally:
print('\nCLOSING SOCKET')
sock.close()

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