Does macOS Sierra run Xcode 7.x?
Is Xcode 7.x functional running macOS Sierra to submit builds to iTunes Connect?
Solution 1:
Submitting apps built with beta versions of an OS or beta versions of Xcode are not officially supported, but you can build apps with a normal version of Xcode on a beta OS by changing the OS version prior to archiving the app inside Xcode.
Solution 2:
You can't submit anything built with a beta OS or beta Xcode. After it becomes live is the only time Apple will accept it for the Store (not including TestFlight).