'App not Installed' Error on Android

I have a program working in the Android Emulator. Every now and again I have been creating a signed .apk and exporting it to my HTC Desire to test. It has all been fine.

On my latest exported .apk I get the error message 'App not installed' when I try to install the .apk. It runs fine on the emulators.

As I have mainly been testing on the emulators and only every now and again exporting to a real phone I am not sure when this happened. What is the likely cause of it not installing on a physical phone but running fine in the emulators?

I have tried rebooting the phone & removing the existing .apk, does not fix the fault.

Solution 1:

Primarily for older phones

I only encountered the App not installed error when trying to install an apk on my phone which runs on 4.4.2 aka KitKat, but my friend did not encounter this error on his phone which runs on 6+. I tried the other solutions such as removing the old/debug version of the app because the apk was a release version, clearing the debug app's data, and even clearing all of my cached data. Then, finally I realized all I had to do was select both signature versions when building my signed apk.

Before I only had V2 (Full APK Signature) selected, but after selecting V1 Jar Signature as well, I was able to successfully install my signed APK on my 4.4.2 device. Hope this helps others!

Solution 2:

For me, On Android 9 (API 28), disabling Google Play Protect from play store app worked the trick, and i was able to get rid of the App not Installed error.

To disable Google Play Protect. Open "Play Store" application => tap on Menu button => select "Play Protect" option => Disable the options "Scan device for security threats".