The main reason for the issue could be
-
You might have turned off “Allow installation from unknown resources”
-
The downloaded .apk is not fully downloaded or corrupted
-
The app is not compatible with the Hardware or version of the OS you are using
Solution: 1
If you are facing this issue in device using android 12. You can fix it by adding android:exported=“true” in AndroidManifest.xml as mentioned below
<activity
android:name=".MainActivity"
android:exported="true"
android:configChanges="keyboard|keyboardHidden|orientation|screenSize|uiMode"
android:label="@string/app_name"
Solution: 2
Instead of shooting in the dark, get the reason for this error by installing it via adb

adb -s emulator-5555 install ~/path-to-your-apk/com.app.apk
Replace emulator-5555
with your device name. You can obtain a list using:
adb devices
Upon failing, it will give a reason. Common reasons and their fixes:
INSTALL_PARSE_FAILED_NO_CERTIFICATES
: Reference
INSTALL_FAILED_UPDATE_INCOMPATIBLE
: Reference