If you are running a retail version of Microsoft Windows (Windows Professional for example) KMS activation will not be possible. In this case we recommend reinstalling a Windows Enterprise version downloaded from IT Shop. Sometimes it may be convenient to convert an existing retail version to an Enterprise Edition with KMS activation. This can be done by using a KMS Client Setup Key for the Enterprise Edition.

See https://docs.microsoft.com/en-us/windows-server/get-started/kmsclientkeys for the appropriate KMS Client Setup Keys and more information on the process.