 <p>FYI, I was able to customize the watch face, using the extension code you provided. No problem there.</p> <p>If you notice the bundle id in the crash log error, the system is reporting a problem with the watchkit app (which contains the watchkit extension).</p> <blockquote> <p>Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Application is required. bundleID: ql.ManaEU.watchkitapp ...</p> </blockquote> <p>You'll need to track down what's wrong with the watchkit bundle. The first place to start would be the Xcode watchkit app build target log. If there are no errors or warnings there, check the iPhone and Apple Watch console logs.</p> <p>If that doesn't point you to the problem, check the <code>Info.plist</code> to make sure those values are valid, and the required keys are present. Also check the watchkit app target build settings.</p> <p>You should be able to use the Version Editor to compare the Xcode project against its initial commit, to see if something was inadvertently changed or deleted.</p>