Has the app already been published in the Play store? In other words, is it an update?
If not:
- Change the current project name (from e.g. "myApp".aia to "my_app".aia).
- Make a backup of the keystore on the AI2 test server and store it in a safe place (on your PC and / or external SD card). (Note: If you haven't created any other apps here yet and published them to the Play Store, you can skip this step!)
- Delete the keystore and reload the browser.
- Create the AAB on the test server.
- Create a new app in the Play Developer console.
- Upload the AAB to the Play Developer console.
If you don't use any (critical) extensions, everything should work fine now.
Otherwise post a screenshot of the error message.