Android 'App Not Installed' Error — How to Fix It

What it means

'App not installed' (sometimes shown as 'App not installed as package appears to be invalid' or 'There was a problem parsing the package') means Android refused to install the APK file.
The usual reasons are: a different signature than the version already on the phone, the file is for a different Android version or processor, the storage is too full, or the APK itself is corrupted from a bad download.
Apps from the Play Store almost never throw this — it's almost always APKs installed by hand.

Affected Models

All Android phones and tablets when sideloading APK files
Common when installing modded apps, beta versions, or apps not available in your region's Play Store
Common with APKs downloaded outside the Play Store from sites like APKMirror, APKPure, or developer websites

Common Causes

An older or differently-signed version of the same app is already installed
APK is for a different Android version (too old or too new)
APK is for a different CPU architecture (ARM vs ARM64 vs x86)
APK file is corrupted from an incomplete download
Storage is too full to install the app
'Install unknown apps' permission is not granted for the file manager or browser
Play Protect is blocking the install
Signed with a key that conflicts with a pre-installed system app

How to Fix It

Uninstall the existing version first.

If you have the same app already installed — even an older or modded version — Android refuses to install over it when the signatures differ.
Settings > Apps > [the app] > Uninstall, then install the APK.
This is the single most common fix.
Re-download the APK.

A partial download silently produces a broken APK that gives this error every time.
Delete the file, redownload it from the original source over a steady connection (Wi-Fi rather than a weak mobile signal), and try again.
While you're at it, check the file size matches what the site says.
Allow install from this source.

Newer Android requires you to allow installs per app — the file manager, browser, or messaging app you opened the APK from.
Settings > Apps > [that app] > Install unknown apps > Allow from this source.
Then open the APK again.
Check the APK is for your phone.

Some APKs are split by architecture (arm64-v8a is the most common for modern phones; armeabi-v7a for older ones; x86 for emulators).
If the site offers variants, pick arm64-v8a unless your phone is more than five or six years old.
The APK also needs to match the Android version — a brand-new app may require Android 12 or 13.
Free up storage.

If the phone is almost full, the install fails with 'App not installed' even though the message doesn't mention storage.
Settings > Storage — clear photos already backed up, old WhatsApp media, and unused apps.
Aim for several gigabytes free for a comfortable install.
Allow it past Play Protect.

Play Protect (Play Store > profile > Play Protect) blocks installs it doesn't recognise.
You can pause it for a single install if you trust the source — but understand that you're losing Android's malware check, and APKs from random websites are a common malware delivery method.
Turn it back on after.
Try a different APK or get it from the Play Store.

If the same APK fails on a clean install with the right architecture, plenty of storage, and Play Protect off, the APK itself is broken — try a different source like APKMirror, which checks signatures.
For apps available in the Play Store, install from there: you avoid this error and you get auto-updates and a malware check.

Frequently Asked Questions

Why does Android say App not installed when I already have the app?

Because the APK you're trying to install has a different signing key than the one already on the phone — Android won't install one over the other.
This happens with modded versions, beta releases, or APKs from a different source than the original install.
Uninstall the existing copy first (Settings > Apps > [the app] > Uninstall), then install the new APK.
Note that you'll lose the app's local data unless you back it up — sign-ins and any saved game progress that isn't tied to a cloud account will need to be redone.