How do I notify users of incoming video calls when an application is terminated or in the background mode?

The implementation of functionality when an application in the background mode or terminated/killed state is implemented in our WebRTC samples.

You can find our video calling samples here - Code Samples | QuickBlox

You can find a Quick Start guide for video calling samples here:
iOS SDK - Quick Start | iOS SDK | QuickBlox
Android SDK - Quick Start | Android SDK | QuickBlox
JavaScript SDK - Quick Start | JavaScript SDK | QuickBlox
React Native SDK - Quick Start | React Native SDK | QuickBlox
Flutter SDK - Quick Start | Flutter SDK | QuickBlox

Please note that you need to configure push notifications for your application/sample:
iOS SDK - Push Notifications | iOS SDK | QuickBlox
Android SDK - Push Notifications | Android SDK | QuickBlox
JavaScript SDK - Push Notifications | JavaScript SDK | QuickBlox
React Native SDK - Push Notifications | React Native SDK | QuickBlox
Flutter SDK - Push Notifications | Flutter SDK | QuickBlox

Additionally, please check our FAQ: How do I configure chat and video calling push notifications and offline messaging?

While integrating the functionality from the sample, you need to configure push notifications as it is described in the guide as well.

Feel free to check our official documentation for more information that will help you to integrate QuickBlox services into your applications / projects or contact our Support team by submitting a ticket if you have any other questions.