Kotlin calling app

I want to make a calling app using the Linphone library. The calling events are triggered by keycode (volume up and down). On top of that, I require some basic UI. Please check the attached slides.

Link to Linphone tutorials and wiki
https://gitlab.linphone.org/BC/public/tutorials/-/tree/master/android/kotlin
https://wiki.linphone.org/xwiki/wiki/public/view/Linphone/