What you seem to need is a background process which listens for incoming calls on your receiving port or what have you – you can then launch the application if the recipient picks up or accepts thew call. The Android Docs have a page on background processes and another page on overriding the call interface for your own app

Good luck with the app

I’m programming a video call app and everything seems to be working. There is only one problem. When one person calls another, the activity “Calling activity” (of the called person) opens only if the person who has been called has opened / opened the application (not when the app is closed). I would like to find a way that when one person calls another even if that other person has the app closed it still opens. How could I do? I leave you my callingactivity code
https://codeshare.io/ar0yxE