In fact, you need to create a new distribution profile specific to Ad Hoc Deployment. This can be found in the classic member center, but this is a new type of certificate.
Then you can choose which devices can be used to test the application, since ou will work with the developer profile.
And the newly created certificate will be available when you export your package from the Organizer in the usual way.
Alternatively, you can use the TestFlight solution provided by Apple with iOS 8 to allow your user to have access to prepayment.

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