There are a lot of potential causes of this problem. Make sure you have the certificate with its private key and the provisioning profile, and that they’re set in Xcode. But if you’ve tried everything else, then make sure you’ve done:
Build -> Clean All Targets
That fixed it for me.
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I had this exact problem! Everything was set up correctly, and Build -> Clean All Targets ALSO did not work. However, what worked for me was rebooting XCode! Sometimes it’s the smallest things that get you!
I also had this, got it working by uninstalling the app I was building from the iPhone. Window/Organizer in Xcode.