VPP applications failing to deploy due to "VPP internal error"

VPP is configured and applications are showing up in XMS console, however failing to deploy to devices

If you drill into the device and look at the Delivery Groups sending installation command fails due to

VPP internal error

Looking in the XMS logs shows the following error message:

2017-02-22T05:04:18.977+1300 |  [UID=364960,usr=user@domain,dev=11661] |  WARN | http-nio-10443-exec-10937 | com.sparus.nps.apple.push.ApplePush | VPP assignment error while trying to install app [resId=737, resPkgDefType='EXT_APP_PUSH']
com.citrix.ios.vpp.wsclient.VPPClientException: ErrorCode returned by Apple: {code=9622, reason='Invalid authentication token'}
	at com.citrix.ios.vpp.wsclient.request.VPPRequest.doRequest(VPPRequest.java:76)
	at com.citrix.ios.vpp.wsclient.request.ManageVPPLicensesByAdamIdSrvRequest.execute(ManageVPPLicensesByAdamIdSrvRequest.java:187)
	at com.citrix.ios.vpp.wsclient.internals.VPPLicenseManagerImpl.associateVppLicenceToDevice(VPPLicenseManagerImpl.java:426)

There is an authentication issue with the Apple VPP portal.
Log into the apple VPP portal on https://vpp.itunes.apple.com and re-download the VPP token.
In XMS console go into Settings -> iOS Settings
Edit the VPP account in question and paste in the new VPP token and re-enter the login credentials
Save the settings
After this the VPP applications should start pushing down again

List of VPP error codes available here: