iOS9 Untrusted Enterprise Developer with no option to trust
In iOS 9.1 and lower, go to Settings - General - Profiles - tap on your Profile - tap on Trust button.
In iOS 9.2+ & iOS 11+ go to: Settings - General - Profiles & Device Management - tap on your Profile - tap on Trust button.
In iOS 10+, go to: Settings - General - Device Management - tap on your Profile - tap on Trust button.
Do it like this:
Go to Settings -> General -> Profiles - tap on your Profile - tap on the Trust button.
but iOS10 has a little change,
Users should go to Settings - General - Device Management - tap on your Profile - tap on Trust button.
Reference: iOS10AdaptationTips
For iOS 9 beta 3,4 users. Since the option to view profiles is not viewable do the following from Xcode.
- Open Xcode 7.
- Go to window, devices.
- Select your device.
- Delete all of the profiles loaded on the device.
- Delete the old app on your device.
- Clean and rebuild the app to your device.
On iOS 9.1+ n iOS 9.2+ go to Settings -> General -> Device Management -> press the Profile -> Press Trust.