With the release of iOS 12.1.1 some changes will be made in the way you install configuration profiles on iOS devices, adding a few simple steps in the process.
In this example we will use on-device enrollment to outline this process:
After you download your profile you're shown the following:
Afterwards you will have to navigate to the Settings App of the device and go to General > Device Management, here you'll see the following:
Press install and you'll be shown the details of the profile:
Press install again and you're met with one final screen:
After pressing install the management profile will install and you're good to go.