Why does calling closed_callback not working in my python eel program?

Question

I have been trying to make a app using python eel for my ui. I have been finding when i close the ui window, the progarm does not stop. So I added close_callback. This has not helped and the app still runs when you close the ui window.

Code:

eel.init("ui")
def close_callback():
    exit()

eel.start("index.login.html", close_callback=close_callback ,disable_cache=True,block=True)

Thanks