When trying to upload an app to App Store in Xcode (7.1) I\'m prompted with this error message:
iTunes Store operation failed. You are not authorised to u
I've faced the same issue (account is attached to several iTunes providers) when I've downloaded Application Loader from iTunes Connect. The link on iTunes Connect download the version 3.0 of application loader that not supports multi-accounts.
To download the latest version and use multi-accounts you should download the latest version of Xcode. Application Loader is part of Xcode (Xcode > Open Developer Tool > Application Loader). You can download Xcode directly from the Mac App Store.
For more information on this delivery mechanism, see the Application Loader User Guide.