Can't submit apps to AppStore: ERROR ITMS-90534: "Invalid Toolchain

Question

ERROR ITMS-90534: \"Invalid Toolchain.

New apps and app updates must be built with the public (GM) versions of Xcode 6 or later, macOS,

Answer 1

I was finally able to resolve this issue by downloading XCode 8.2.1 from the App Store.

Re-archiving the project and submitting as usual.