When trying to upload an App to iTunes connect in Xcode 8.3.3, I get the error:
iTunes Connect access for \"Team-Name\" is required. Add an account in
This goes along with the other answers, eventually I had to export it and deliver the ipa with Application Loader.
However, Application Loader didn't initially work for me. I had to go into my apple id account (appleid.apple.com) and add an application specific password. Then I signed out of Application Loader and signed back in with the application specific password.
As far as I know, xCode doesn't let you sign in with an application specific password. My guess is that Apple broke authentication via regular passwords on their backend, but didn't break application specific ones.