Your iPhone is not available. Please select a different device and try again [closed]

I'm getting the following error when I try to build my Watch OS 2 app on my iPhone (iOS 9.0b2) which is paired to my Apple Watch (watchOS 2.0b2).

Your iPhone is not available. Please select a different device and try again.

I've tried all the obvious things, restarting iPhone, Watch, Mac, etc. All my software is updated to the latest version and my watch is paired to my iPhone. Does anyone have any ideas?

Why is my iPhone saying Trusted device List is not available?

All your devices that are signed into your Apple ID that is being used on that device should be listed at the bottom of Apple ID setting in Settings. If you can't see any of them, then the device you're looking at is signed into a different Apple ID than your other devices.

Connect the phone and open iTunes. Once the "Trust this iPhone" sequence is complete via iTunes, the phone will be recognized in Xcode.