Very very basic python-binance ThreadedWebSocketManager example does not work... why?

I have an application that uses the binance api to trade and do some other stuff. The app worked fine for like 2 years, but one day it stopped working. So i decided to create a basic script to validate the core functionality of the api. I did everything exactly like its described in several offical docs and tutorials but its still not working as expected. Here is my code:

from binance import Client, ThreadedWebsocketManager

api_key = 'my_key'
api_secret = 'my_secret'

client = Client(api_key, api_secret)

def process_message(msg):
    print("message type: {}".format(msg['e']))
    print(msg)

twm = ThreadedWebsocketManager(api_key=api_key, api_secret=api_secret)
twm.start()

ret = twm.start_kline_socket(callback=process_message, symbol='BTCEUR', interval='1m')
print(ret)

twm.join()

So, what happens at all? The twm is created and my print statement returns: btceur@kline_1m
thats all. I expected the script to call the process_message func every 1 minute, but it does not get called after a 1 min session has completed. I have seen some similar troubles with older versions, have tried all possible solutions but I wasn´t able to fix it. I am using the latest python-binance version, v1.0.19 - 2023-08-11 and python 3.12.3