Enable camera permissions: [Settings]-[Apps & notifications]-[App permissions]-Facebook/Whatsapp -[camera]-[allow] (For Android O: [settings]-[Apps]-[App permissions]-Facebook/Whatsapp -[camera]-[allow]).

          Note: Image is just for demonstration, it may be different from the actual situation.

• If you notice the same issue, check the camera function if it is OK.
• If your problem has not been solved, try to update your phone to the latest software version and reboot phone to check if it is OK.
• If the issue persists, reset your device after back up, go to [Settings]-[System]-[Reset options]-[Erase all data (Factory reset)] (For Android O: [Settings]- [Backup &reset]-[Factory data reset]-[Reset phone]).