With the release of iOS 9, testers will be required to “trust” your organization’s Apple Enterprise developer certificate, one-time, before running Beta distributions. Testers will see the message “Untrusted Enterprise Developer” when running an app from an untrusted certificate and can trust it by following the steps outlined below on their device.
Follow this steps:
1. Navigate to Setting -> General –> Profiles
2. Select the developer certificate in the “ENTERPRISE APP” section
3. Press “Trust [Developer]”
4. Select “Trust”