DEP registration must be deactivated
When an iOS device needs to be repaired it cannot have an active DEP registration with an MDM server.
If your MDM server supports DEP deactivation you can use this.
But when you have an MDM solution that works with, for example blueprints, you cannot deactivate a DEP registration for a device.
To prevent a device registered with DEP from connecting to your MDM server during an activation you can do the following.
Under Deployment Programs choose "Device Assignment"
Select "Serial Number"
In the textfield under the button you can enter 1 or more devices by serial number.
Separate multiple devices with a comma.
From the pulldown menu select "Release devices".
Do not forget to re-assign the device(s) to your MDM server in DEP when it returns from repair.
All the actions stay the same as mentioned above except for the choice in the pulldown menu under Step 2.
Now you have to choose for the option "Assign to Server".