Make sure that your phone is connected to network.
Check the settings of your phone.
Use Redmi 5(Android 7.1.2) as example：
1. Go to Settings -- Notifications & status bar -- App notifications -- Letstalk -- enable show notification, Priority, App icon badge, Lock screen notification, Sound, Vibration, Notification light.
2. Go to Settings -- Battery & performance -- Choose apps -- Letstalk -- choose No restrictons.
3. Go to Settings -- System apps- -- Security -- Boost speed -- Lock apps -- Enable Letstalk.
4. Click the menu button and slide down the application page until you can a lock icon in the upper corner to allow applications to run in background. Then the application will keep running in background.
