Have you purchased App Volumes as a Standalone SKU or Horizon Enterprise?
If part of Horizon, please check this document: https://www.vmware.com/files/pdf/products/horizon/VMware-Horizon-FAQ.pdf
Q. How is App Volumes (formerly of Cloud Volumes) licensed in Horizon 6?
App Volumes is licensed with Horizon Enterprise on a per named user or per concurrent connection basis and will map directly to the licensing of the overall bundled offering.
In a concurrent setting, customers need to ensure that they do not exceed the maximum agreed upon active and powered on sessions.