What causes this Android APK Upload error: “Non-upgradable APK”

Question

I have an Android APK in the Google Play store with an Target SDK of 23.

I have released a new version (same target SDK) and Google shows me this error:

If I

Answer 1

I ran into this issue because in my cordova config.xml the previous version was 0.0.51 and the new version was 0.0.6. But in the playstore console, those numbers were converted to 51 and 6 for the APK number. One can't "upgrade" from 51 to 6. So I changed the xml to be 0.0.60, which made the APK number 60, and voila, I can update from 51 to 60.