"The Android App Bundle was not signed." On Google Play Console

I have attempted to upload a new release as I have updated some settings and I am getting the following error when I attempt to upload the AAB file: "The Android App Bundle was not signed." I am using Google Play App Signing, so I thought this would be taken care of automatically. The Median documentation states "Median signs each app with a randomly generated release key. If you need to create release builds from source code, please contact support to obtain your release key." Is there something I am missing here? Do I have to create a new App every time I want to upload a new build?