You can send invitations to device users manually in Configuration Management by following the guide below.
You can only send VPP invitations to devices with iOS 8 or higher.
The user signed in to the device will receive a notification on this device asking to join the Volume Purchase Program. If the invitation is accepted, the users Apple ID will be associated with your VPP and the status of the VPP User in System Administration will change status from Registered to Associated.
The simplest way of associating a VPP account with your users devices is using an Enrollment Configuration. Correctly configured this will automate the linking process fully, and devices will be able to get licensed Apps from one of the VPP accounts already linked to CapaInstaller and/or give the user the option to choose one during enrollment. As part of the device enrollment an invitation to the VPP will be sent to the device, and a VPP User will be created in your VPP Account with the status 'Registered'. Once the user accepts the invitation, the VPP User in System Administration will change status to 'Associated', and will be linked to the Apple ID of the user who accepted the invitation on the device.