How can I use CallKit to take video chat calls

Question

I have a Xamarin.Forms application that implements video chat. For now, a video call is made by sending push notifications using UIKit, and is answered by touching the push notification. I would like to use a native iOS telephony feature, that would let the user make a real phone ringing etc. I heard that it could be done using Callkit, but I can't find any example or explanation on how this can be done. Or maybe there is some way other than Callkit? Basically, answering the call (like with a common phone call) should replace touching the notification.