If the Velox App does not ring when your VIVO device is on sleep mode or on lock screen.


1. Allow the app to keep running even during high power consumption. 

Step 1. Go to System Settings > Battery.

Step 2. Go to High background power consumption.

Step 3. Find the Velox App in the list and enable the high battery consumption



2. Lock the app in the taskbar 

        Apps locked in  taskbar are safe from getting terminated when they run on background.

        Step 1. Swipe up in your home screen while the app is open in the background, 
        and swipe the app icon down.
    
        Step 2. Tap the lock icon.
    
        Step 3. Done - now the app is locked in the taskbar.


Another layout for locking the app.

    Step 1. Access App Drawer/App Switcher

Step 2. Choose "Lockdown/Lock" in the top right submenu.

    Step 3. Done - now the app is locked in the taskbar. 


This information is based on THIS VIVO help site.