To enable push notifications, you need to add a VAPID key to your environment variables.
- Go to your Firebase Console.
- Navigate to Project Settings > Cloud Messaging.
- Under the "Web configuration" section, find **Web Push certificates** and click **Generate Key Pair**.
- Copy the generated key (the long string).
- Open the `.env` file in your project and paste the key: `NEXT_PUBLIC_VAPID_KEY=YOUR_KEY_HERE`
- Restart your development server.