First of all you need to find the correct KMS key. You should not use the Windows 10 KMS key that you find in the download section of Microsoft Volume Licensing Center. To find the correct key you need to go to “Relationship Summary” located in the Licenses menu in Microsoft Volume Licensing Center. In the summary, click on your active license id and choose the “Product Keys” tab. Here you need to locate “Windows Srv 2012R2 DataCtr/Std KMS for Windows 10”. Copy that key.
If you try to install this key in VAMT you might encounter this error.
The solution is to first uninstall the current KMS key from the server and then install the new key using command line with the following commands:
Uninstall product key
PS C:\Windows\system32> .\cscript.exe .\slmgr.vbs /upk
Install the new key
PS C:\Windows\system32> .\cscript.exe .\slmgr.vbs /ipk XXXX-XXXX-XXXX-XXXX-XXXX
Restart the Software Protection Service
PS C:\Windows\system32> Restart-Service sppsvc
Check that the new newly installed key is the correct key
PS C:\Windows\system32> .\cscript.exe .\slmgr.vbs /dlv
The output of the command should say that your activation channel is “VOLUME_KMS_2012-R2_WIN10”.
If this is a new KMS server the server needs 25 or more license requests before it starts activating Windows (or 4 or more Windows Server Requests before it starts activating Server OS’es).