Open the Targets page > Add Targets > Internal targets
Click 'View configuration keys'
Copy the 'Prefix'
Your DeviceName is comprised of your Prefix and your TargetName (no spaces!)
DeviceName = Prefix_TargetName
For example if your prefix is DQEGBQUAAAc and you would like your target to show as paul-laptop in the portal, then your DeviceName would be: