Problems with Push Notification and Django (vapid_private_key)

I was able to reproduce an example with the pywebpush repository to make Push notification. After breaking my head to understand, I managed to do it. However, when I tried to integrate with my django project, it did not roll. I believe it's something related to the private_key.pem file I create.

Error:

...
File "/Users/myuser/.virtualenvs/myenv/lib/python3.6/site-packages/pywebpush/__init__.py", line 359, in webpush
    vv = Vapid.from_string(private_key=vapid_private_key)
  File "/Users/myuser/.virtualenvs/myenv/lib/python3.6/site-packages/py_vapid/__init__.py", line 142, in from_string
    return cls.from_der(pkey)
  File "/Users/myuser/.virtualenvs/myenv/lib/python3.6/site-packages/py_vapid/__init__.py", line 99, in from_der
    backend=default_backend())
  File "/Users/myuser/.virtualenvs/myenv/lib/python3.6/site-packages/cryptography/hazmat/primitives/serialization.py", line 28, in load_der_private_key
    return backend.load_der_private_key(data, password)
  File "/Users/myuser/.virtualenvs/myenv/lib/python3.6/site-packages/cryptography/hazmat/backends/multibackend.py", line 323, in load_der_private_key
    return b.load_der_private_key(data, password)
  File "/Users/myuser/.virtualenvs/myenv/lib/python3.6/site-packages/cryptography/hazmat/backends/openssl/backend.py", line 1018, in load_der_private_key
    password,
  File "/Users/myuser/.virtualenvs/myenv/lib/python3.6/site-packages/cryptography/hazmat/backends/openssl/backend.py", line 1160, in _load_key
    self._handle_key_loading_error()
  File "/Users/myuser/.virtualenvs/myenv/lib/python3.6/site-packages/cryptography/hazmat/backends/openssl/backend.py", line 1229, in _handle_key_loading_error
    raise ValueError("Could not deserialize key data.")
ValueError: Could not deserialize key data.

push.py

from pywebpush import webpush, WebPushException
from apps.user.models import User, PushNotification
from django.conf import settings
import os

def push_notification(message, user = None):
    if not user:
        all_users = PushNotification.objects.all()
        for au in all_users:
            try:
                webpush(
                    subscription_info={
                        "endpoint":au.endpoint,
                        "keys":{
                            "p256dh":au.p256dh,
                            "auth":au.auth
                        }},
                    data=message,
                    vapid_private_key=os.path.join(settings.PRIVATEKEY_DIR, 'private_key.pem'),
                    vapid_claims={
                        "sub": "mailto:[email protected]",
                    }
                )
            except WebPushException as ex:
                print("I'm sorry, Dave, but I can't do that: {}", repr(ex))
    else:
        _user = PushNotification.objects.filter(user = user)
        if _user.exists():
            _user = _user[0]
            subinfo = {
                "endpoint":_user.endpoint,
                "keys":{
                    "p256dh":_user.p256dh,
                    "auth":_user.auth
                }
            }
            print(subinfo)
            try:
                webpush(
                    subscription_info=subinfo,
                    data=message,
                    vapid_private_key=os.path.join(settings.PRIVATEKEY_DIR, 'private_key.pem'),
                    vapid_claims={
                        "sub": "mailto:[email protected]",
                    }
                )
            except WebPushException as ex:
                print("I'm sorry, Dave, but I can't do that: {}", repr(ex))

I am generating the files according to the repository they indicate: vapid

The problem is that I was able to make Python work only. Now, calling that same Django python, it did not roll .. I start the dictionary it generates to check if it has any errors but no, it does not. It's the same.