in Android Studio I generated a signed APK with keystore and so on. While installing the APK onto a device it fails with \'App could not be installed\' and in Android Monito
Try to signed your APK with version 1. Version 2 signed APK only compatible from 7.0 so it will not working on below 7.0 devices or try to generate v1 and v2 version APK.
[ Note: When you generate signed apk for above 7.0 devices and below 7.0 devices then please check v1 and v2 both option. ]
Here is the reference link for more about V2 version and here is the link for overview.
Try this out and Your issue will resolved.