Django-paypal внезапно перестает получать сигналы от Paypal

Я работаю над интеграцией Paypal в мой проект Django с использованием пакета Django-Paypal. Я успешно настроил все, и он работал, но внезапно сигналы из PayPal прекратились.

Какая проблема может возникнуть?

Вот что я сделал:

из view.py:

def payment_process(request):
minutes = int(request.user.tagging.count()) * 5
testhours = minutes / 60
hours = str(round(testhours, 3))
# pdb.set_trace()
# What you want the button to do.
invoice = generate_cid()
userInfo = {
    "name": str(request.user.first_name + ' ' + request.user.last_name),
    "hours": str(hours),
    "taggedArticles": str(request.user.tagging.count())
}
paypal_dict = {
    "business": settings.PAYPAL_RECEIVER_EMAIL,
    "item_name": "Certificate of Completion from Nami Montana",
    "custom": userInfo,
    "invoice": str(invoice),
    "amount": "5.00",
    "notify_url": "https://6fd5e31b.ngrok.io/users/paypal/",
    # "return_url": "https://6fd5e31b.ngrok.io/users/profile/",
    "cancel_return": "https://6fd5e31b.ngrok.io/users/cancel/",
}
print(paypal_dict)
# Create the instance.
form = PayPalPaymentsForm(initial=paypal_dict)
context = {"form": form}
return render(request, "users/generateCert.html", context)

из urls.py:

urlpatterns = [
   url('^paypal/', include('paypal.standard.ipn.urls')),
   url('^profile/buildCertificate/$', views.CertificateProcess.as_view(), name='certificate'),
   url('^cancel/$', views.payment_canceled, name='cancel'),
   url('^done/$', views.payment_done, name='done'),
   url('^process/$', views.payment_process, name='payment'),
]

Из signal.py:

def show_me_the_money(sender, **kwargs):
ipn_obj = sender
custom = ipn_obj.custom
# Undertake some action depending upon `ipn_obj`.
if ipn_obj.payment_status == ST_PP_COMPLETED:
    print('Get success signal')
    user_info = ast.literal_eval(ipn_obj.custom)
    if int(user_info['taggedArticles']) > 11:
        # here i need to generate and send a pdf file to the user in a new tab
        pass
else:
    print('Get fail signal')


payment_was_successful.connect(show_me_the_money)

Update: When I have tested it with live IPN sandbox it returns IPN was sent and the handshake was verified

Payment is successfully depositing to the PayPal sandbox merchant account, only the signal is doing some problem.

Помоги мне, пожалуйста!

Заранее спасибо!