While we are using the official Amazon API for the authentication process, it's possible that we cannot access your "Amazon Music" account with the dedicated Amazon Music API.
That's why even if the login process seems done successfully, Amazon Music is then disconnected on Soundiiz.
Unfortunately, there's nothing we can do about it. Be sure to have accepted all "Music" scopes during the login process and double-check that your Amazon Music is well configured.
If you still have the issue; please contact Amazon support directly to get more information.