- The user does not come online before the notification expires.
- The browser does not run on the user’s device.
- Communication between FCM, the browser, and the operating system fails.
Operating system settings do not contribute to this difference. When a user grants web push permission in the browser but turns off notifications for that browser at the operating system level, the browser receives the notification, so MoEngage counts the impression and tracks the Notification Received Web event, even though the operating system suppresses the on-screen display. MoEngage also counts this user as subscribed and reachable for web push. For more information, refer to Browser Permission Versus OS-Level Notification Settings.