Hi.
So, a things to look for.... I don't quite know where you are in the process, but I hope this helps
1. Check your licenses: If you don't have enough licenses, enrollment will fail
2. Check that your iPads have a WiFi profile installed on them before you begin, or at least part of the Prepare process
3. Check that you have a default DEP profile set up in DEP page
4. For your MDM server in AC2 prefs, ensure that you have the full URL that's in Systems Manager > Add Devices