"This network is on the DVS which is not part of selected Service Mesh. Hence it can't be extended"
This issue occurs when the Overlay transport zone is not selected while configuring the Compute Profile.
https://<hcx-manager/Interconnect --> Compute Profiles --> Edit Compute Profile --> Select Network Containers Eligible for Network Extensionre-sync the specific Service Mesh to update the changes done in the compute profile.https://hcx-manager/Go to --> Interconnect --> Service Mesh --> Choose the specific service mesh --> ResyncFor other restrictions and limitations, please review the "Restrictions and Limitations for Network Extension" section in the VMware HCX Product Documentation.