Untrusted Enterprise Developer (Since iOS 9)
iOS 9 has increased the security around Over-the-Air (OTA) installations. You must now indicate on your device that you trust the Apple Enterprise developer certificate before you can run the installed build.
You need to perform these steps only once before running any apps from a trusted developer:
Go to Settings
Open General > Device management (or in iOS 9.1 General > Profiles)
Tap on the developer’s name from the list of possible options.
Press Trust “Company name” button
You should be able to launch any apps from this developer now.
Pre-existing bundle identifier on the device
When installing a build if you find tapping on the install button doesn’t seem to do anything this is most likely caused by having an AppStore version of your app already installed on your device.
This is caused by the OS and the only workaround is to uninstall the AppStore version or use a temporary bundle identifier for the MBM build.