INSTALL_FAILED_UPDATE_INCOMPATIBLE

[iddq]

APK cannot be installed after resign.

java -jar uber-apk-signer-1.2.1.jar --allowResign -a

adb install -r
Failure [INSTALL_FAILED_UPDATE_INCOMPATIBLE]

Android 6.0.1

for first look the original APK contains CERT.SF and CERT.RSA

[MarcMil]

That's to be expected when the certificate is different from the original app. You cannot install an app with one package name on the device when an app with the same package name signed with a different certificate is already installed.

[patrickfav]

As @MarcMil already stated, uninstall the app first. Then install with the new certificate - this is by design and a security measure of Android.

[iddq]

On older android systems like 6.0.1, uninstalling the app from GUI is not enough. We have to uninstall it by adb uninstall command even that is uninstalled from GUI before because the certificate somehow remains on the system.