documentation refer to an none supported parameter 

    (.venv) [kni@ocp-edge77 ocp-edge-auto_cluster]$ hcp -v
hcp version openshift/hypershift: 707991204d698dfa1e6ee03d14204d1a376a7435. Latest supported OCP: 4.15.0

https://github.com/stolostron/rhacm-docs/blob/2.9_stage/clusters/hosted_control_planes/scale_nodepool_hosted_bm.adoc#adding-node-pools:~:text=%2D%2DagentLabelSelector

Follow the documentation steps for adding node pools (agent) :

https://github.com/stolostron/rhacm-docs/blob/2.9_stage/clusters/hosted_control_planes/scale_nodepool_hosted_bm.adoc#adding-node-pools
 

in the documentation, there is --agentLabelSelector '{"matchLabels": {"size": "medium"}}' 

Which is not supported by latest version:

(.venv) [kni@ocp-edge77 ocp-edge-auto_cluster]$ hcp create nodepool agent --help 
Creates basic functional NodePool resources for Agent platformUsage:
  hcp create nodepool agent [flags]Flags:
  -h, --help   help for agentGlobal Flags:
      --cluster-name string             The name of the HostedCluster nodes in this pool will join. (default "example")
      --name string                     The name of the NodePool.
      --namespace string                The namespace in which to create the NodePool. (default "clusters")
      --node-count int32                The number of nodes to create in the NodePool. (default 2)
      --node-upgrade-type UpgradeType   The NodePool upgrade strategy for how nodes should behave when upgraded. Supported options: Replace, InPlace
      --release-image string            The release image for nodes; if this is empty, defaults to the same release image as the HostedCluster.
      --render                          Render output as YAML to stdout instead of applying.
(.venv) [kni@ocp-edge77 ocp-edge-auto_cluster]$ 

    (.venv) [kni@ocp-edge77 ocp-edge-auto_cluster]$ hcp create nodepool agent   --cluster-name $CLUSTER_NAME   --name $NODEPOOL_NAME   --node-count $WORKER_COUNT   --agentLabelSelector '{"matchLabels": {"size": "medium"}}'
Error: unknown flag: --agentLabelSelector
unknown flag: --agentLabelSelector

  command ends successfully