The recipient's phone app is closed. How does a new chat message reach them?

Options

• ✗ Keep the app's WebSocket open in the background forever
• ✓ Send a push notification through APNs or FCM; the app fetches messages when opened Correct
• ✗ Retry the WebSocket every second until the app opens
• ✗ Send an SMS for every message

Why

Mobile operating systems close background connections to save battery, and only their own push services (APNs for iOS, FCM for Android) can wake the device.

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