Alright.. I think things are working right for you now on all your sites. Please test
The issue looks to be that the "Valid OAuth Redirect URIs" setting was not set at all. That should be the URL that the user is sent back to after they authenticate your app. That setting is now required for all apps, but older apps (like your 'n' app) still have the option available (Use Strict Mode for Redirect URIs) to not require it to be set.
The Autotune app *should* set this setting for you automatically, which it doesn't seem to have done. I've set them for you in the s and b app though and things should work. Of course, if you run into issues, let me know or double check that I entered the URL correctly. Also, if your site is accessible in various ways (like with or without www and with or without http / https, you should enter all those variations as options).
I hope that helps, but should you need anything else, please let us know.
Thanks,
Alex