Q: For BYOL, do we need to use Mac Address or HostID for licensing VPX on Azure ?

A: For generating licence for a VPX it's HostID is used, it's usually the Mac Address of Loopback interface but in case of Azure its not the same, it will be a string starting C1xxxxxx. To find the hostID run the command "lmutil lmhostid" on shell prompt. 

Note: The above applies to platform license, for Gateway universal licence hostname is used, for more info on licensing please see https://docs.citrix.com/en-us/citrix-gateway/13/licensing.html