fix

app.py

@@ -11,6 +11,7 @@ import aiohttp
 from aiohttp import web
 from dotenv import load_dotenv
 from pywebpush import webpush, WebPushException
+from cryptography.hazmat.backends import default_backend
 from cryptography.hazmat.primitives import serialization
 from cryptography.hazmat.primitives.asymmetric import ec