I am using `agora.io` to create a calling app. It's possible to talk when the app starts, but once you close the app the call will end. With Facebook Messenger, Skype, and whatsAPPp, you can use other apps while keeping a call. What should I use to keep the app running in the background like this?

[![enter image description here](https://i.stack.imgur.com/GbTIA.jpg)](https://i.stack.imgur.com/GbTIA.jpg)