Xcode fails to install watchOS app onto Apple Watch device

Question

Xcode "Run" operation fails to install a watchOS app on a real Apple Watch device with error description:

The host is not paired with the device.

Context:

• First time ever trying to install a watchOS app from Xcode onto an Apple Watch device for testing/debugging
• The watchOS app is an official Apple SwiftUI tutorial example
• Assume latest versions of MacOS, Xcode, watchOS, Watch device, etc.
• The selected scheme is the watchOS app target
• The selected device is "[my Apple Watch name] via [my iPhone name]"
• The Apple Watch is in fact paired with the companion iPhone, despite what the Xcode error says

Answer 1

What needs to be done is restarting both devices, iPhone and paired Apple Watch, connect iPhone to computer with cable. When the trust/don't trust notification appears on the Apple Watch or iPhone obviously choose 'trust'. Then the app will install again.

What it stops from running on your watch sometimes is if you have a simulator debug session open still. It says it can't install because there is another debug session running (but not on your watch..)! Closing this simulator session will allow you to install on your watch.

Other times xCode is building fine and thinks it's running the app on your watch, but it runs an old version and you don't see any changes made. Then you have to delete the app from your Apple Watch.

What also sometimes stops it from running on the Apple Watch are in Xcode the Preferences->Accounts->Profiles. Installing them manually will help in that case.

If nothing works uncouple your apple watch from your iPhone and recouple again.

Why isn't this still been resolved? I see people complaining about it for several of years now. Is this bug only related to standalone apps?

Answer 2

The Apple Watch has not yet trusted this particular Xcode, Mac, developer account, or app. The Apple Watch should have received a "trust/don't trust" notification, but did not; this may be a bug on Apple's part.

However, we can force the notification to pop up by simply restarting the Apple Watch device. The Watch should receive the notification immediately upon restarting. Click "Trust" in the notification on the Watch. Then retry, from Xcode, the "Run" operation. The watchOS app should now install OK on the Apple Watch device.