[Fixed]-Django m2m_changed signal is never called

I found my mistake in this section of Django the documentation.
From the beggining, my apps configurations were never called!

Actually, to register an app correctly, I have two methods:

method 1

INSTALLED_APPS = ['badges', ...]

and declaring in __init__.py: default_app_config = 'badges.apps.BadgesConfig'

method 2

INSTALLED_APPS = ['badges.apps.BadgesConfig']

my mistake

I was using the INSTALLED_APPS = ['badges', ...] without declaring anything in __init__.py

I think maybe Django could display a warning when it notices that apps.py is in a folder app but never used.