I just created an app with App Inventor 2. I clicked on Build and then saved it on Computer. Then uploaded the .apk on my google developer console account.
But when the upload completes, it says:
Upload failed
Check the symbol in your apk-file. It is not valid
German Original: "Hochladen fehlgeschlagen Überprüfe das Symbol in deiner APK-Datei. Es ist nicht gültig."