Under certain conditions, you might be unable to assign a license to an ESXi host.
You try to assign a license to an ESXi host, but you cannot perform the operation and you receive an error message.
You might be unable to assign a license to an ESXi host because of the following reasons:
The calculated license usage for the host exceeds the license capacity. For example, you have a vSphere license key with capacity for two CPUs. You try to assign the key to a host that has four CPUs. You cannot assign the license, because the required license usage for the host is greater than the license capacity.
The features on the host do not match the license edition. For example, you might configure hosts with vSphere Distributed Switch and vSphere DRS while in evaluation mode. Later, you try to assign vSphere Standard license o the hosts. This operation fails because the vSphere Standard edition does not include vSphere Distributed Switch and vSphere DRS.
The host is connected to a vCenter Server system that is assigned a license that restricts the edition of the license that you want to assign.
Assign a license with larger capacity.
Upgrade the license edition to match the resources and features on the host, or disable the features and resources that do not match the license edition.
Assign a vSphere license whose edition is compatible with the license edition of vCenter Server.