React-Native - Why can't I run my app on old Android devices?

By default when you type react-native run-android in the console react native tries to use a command adb reverse to tell the phone how to communicate with the development server running on your computer.

adb reverse command was added in Android 5.0, so if you want to run the app on an older Android you need to connect to the server via Wi-Fi.

Please find more information here.