Check Signing Key: Ensure the APK is signed with the correct key. For distribution, always sign your app with a release key.

Uninstall Previous Versions: Remove any app with the same application.

Use Compatible SDK: Verify that the devices have Android versions between your minSdk (21) and targetSdk (30).

Generate Release APK: You can create a signed release APK via Android Studio (Build > Generate Signed Bundle / APK).

Enable Installation from Unknown Sources: Ensure the devices allow installing apps from unknown sources.

Test on Multiple Devices: Verify compatibility across various devices.

try to install the file from the file manager.