I also had the same problem, but found a solution. What did the trick for me was creating an AppStore Connect API key and use it with notarytool store-credentials (using the --key --key-id --issuer options). Using that method of authentication works, I managed to notarize 2 dmg images.
bitgammasas
Users receive reputation points by contributing quality content to the forums.
Posts include post and replies published on the forums.
Post authors can mark replies as Accepted to indicate successful solutions.
Apple Developer Forums admins can mark replies as Apple Recommended to indicate an approved solution