iPhones are not equipped with NFC reading capabilities. If you would like to register your watch you need an Android device with NFC reader. You cannot register or authenticate watches with the Apple app. The Apple app will only allow you to create an account or review watches you have added to your account in case you have registered the watch with a borrowed Android device. As soon as Apple comes out with NFC reading, we will of course also allows authentications and registrations with iPhones.