Attribute application@allowBackup value=(false) from AndroidManifest.xml is also present at [:barcodescanner:] AndroidManifest.xml value=(true)

You have to tell the compiler to ignore the attribute from the external library. The way to do that is to add this line in application tag:

tools:replace="android:allowBackup"

PS: To access the tools add xmlns:tools=”http://schemas.android.com/tools” in the manifest tag at the top.