push notifications stop working on ios 13 and 14

Push notifaction does not work on ios 13 and 14 devices. We have a python server and using pyfcm to send notifications through firebase (using a key). All is working fine on ios 12.4 development and production and all test notifucation for more then one device , one device and directly thorugh apns works even on ios 14 device

here some of the server's code :

 extra_kwargs = {
    'mutable_content': True,
    'apns_push_type': 'alert'

if status_code == 200:
        response = push_service.notify_single_device(registration_id=device_token, 
message_title=message_title, message_body=message_to_send, 
content_available=True, extra_kwargs=extra_kwargs )

what do you think is the reason ? any recommandation to other packages that worksare welcome too