Do you have a paid Individual Developer Account? I'll assume you don't and you're wanting to use free provisioning...confirm your process in that case.
Free provisioning/testing on your device:
• From within Xcode 7.x or higher (Mac only), navigate to “Xcode—->Preferences—->Accounts.” Hit the '+' icon below left to add your Apple ID*. After you add your account, it will show within the main account window on the right.
• Select your account, hit the “View Details” button and wait for them to load.
• Now create the 'signing identity' used to create a provisioning profile used for device testing - Hit the “Create” button next to the 'iOS development' label. When completed, hit ‘Done’.
• Connect your device and select it as build destination via the 'active scheme' dropdown to the right of the play and stop icons.
• In target's 'General' tab/settings:
• a. Set app identifier you want for your free profile
• b. Set team id as your apple id
• c. Hit 'Fix Issue' button below the provisioning profile warning
- You may have to ‘Fix Issue' more than once - keep at it so Xcode can step thru them as needed.
• Run your app with your device selected.**
Notes:
- The profile will be valid for 1 week, after which time you will need to recreate a new one.
- There is a limit to how many apps you can build and test to your device.
- Maximum number of devices allowed not known exactly, but if same as paid account, the limit is 100
- What you can/can't do w/free provisioning is listed here:
https://developer.apple.com/library/ios/documentation/IDEs/Conceptual/AppDistributionGuide/SupportedCapabilities/SupportedCapabilities.html#//apple_ref/doc/uid/TP40012582-CH38-SW1
- If this is about creating an .ipa to manually hand off, select Build For Archiving under the project menu, not ‘Run’.
- *If you have, or plan to have, a paid developer account, be sure to use a unique/different apple ID for each account.
- **Free accounts may experience issues launching apps on the watch for the first time.
Workaround: Launch the app manually on the device and click “Trust” when the security sheet appears. You should then be able to launch the app from Xcode.