Unable to receive vídeo Stream from tello drone

I am writhing a python script in order to communicate to my tello drone via wifi.
Once connected with the drone I can send UDP packets to send commands (this works perfectly fine).
I want to receive the video stream from the drone via UDP packets arriving at my udp server on port 11111. This is described in the SDK documentation, "https://dl-cdn.ryzerobotics.com/downloads/tello/20180910/Tello%20SDK%20Documentation%20EN_1.3.pdf".

print ('rnrnTello drone communication toolrn')

print("...importing modules...")

import threading 
import socket
import sys
import time
import platform  
import cv2

print("Modules imported")

print("...Initialiasing UDP server to get video stream....")

drone_videostream = cv2.VideoCapture('udp://@0.0.0.0:11111')

print("Server initialised")

# my local adress to receive UDP packets from tello DRONE
host = ''
port = 9000
locaddr = (host,port) 

print("...creation of UDP socket...")
# Create a UDP socket (UDP Portocol to receive and send UDP packets from/to drone)
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)

# Got drone port and ip adress from network (explained in official SDK documentation)
tello_address = ('192.168.10.1', 8889)

print("UDP socket created")


sock.bind(locaddr)

width = 320
height = 240


def receiveStream() :
    print("...receiving stream...")
    while True :
        ret, frame = drone_videostream.read()
        img = cv2.resize(frame, (width, height))
        cv2.imshow("LiveStream", frame)
        cv2.waitKey(1)
        drone_videostream.release()
        cv2.destroyAllWindows()
        
   
def receiving():
    while True: 
        try:
            data, server = sock.recvfrom(1518)
            print(data.decode(encoding="utf-8"))
        except Exception:
            print ('nExit . . .n')
            break


print ("...initialiazing connection with tello drone...")

message = "command"
message = message.encode(encoding="utf-8") 
sent = sock.sendto(message, tello_address)

print("Connection established")

#create a thread that will excute the receiving() function
receiveThread = threading.Thread(target=receiving)
receiveThread.start()

receiveStreamThread = threading.Thread(target=receiveStream)


while True :
    message = input(str("Enter a command :rn"))
    if message == "streamon" :
        message = message.encode(encoding="utf-8") 
        sent = sock.sendto(message, tello_address)
        receiveStreamThread.start()
    else :
        message = message.encode(encoding="utf-8") 
        sent = sock.sendto(message, tello_address)

When I send the "streamon" command to the drone, I am unable to read the sended UDP packets. I get the following error :

error: (-215:Assertion failed) !ssize.empty() in function 'cv::resize'

This means that the frames are empty, thus, no image received.

Do you know why I dont receive them ?

Thank you very much for your help in advance,
Best 🙂