How can a Network Extension notify or trigger tasks in the main app when it’s backgrounded or killed?

I’m developing a iOS VPN app, and I need to execute a task in the main app even when it’s in the background or killed state. I know the Network Extension continues running during those times. Is there a way for the extension to immediately notify the app or trigger a task on the app side?

How can a Network Extension notify or trigger tasks in the main app when it’s backgrounded or killed?
 
 
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