When you upload an APK, it needs to meet Google Play’s target API level requirements. New apps must target at least Android 10 (API level 29) starting August 2, 2020. App updates have until November 1.
Voltbuilder uses the default level of Cordova, which is currently 9.0.0. That still uses Android API Level 28.
However, it’s easy to override so API Level 29 is used. Add this line to your config.xml:
<engine name="android" spec="9.0.0" />
Your app will now meet Google Play’s requirements.
We expect Cordova to update its default level over the next few days, so this won’t be needed for long.