How to update your KMS server to support Windows 10
First of, your KMS server needs to be running Window Server 2012 R2.
Windows Server 2008 R2 is not supported for activation of Windows 10 clients.
1. On your KMS server, request and install the hotfix KB3058168
(Update that enables Windows 8.1 and Windows 8 KMS hosts to activate a later version of Windows)
you can check if you already have it by running: Get-hotfix KB3058168 in Powershell
2. Then grab your KMS key from your volume license site.
(https://www.microsoft.com/Licensing/servicecenter/default.aspx)
Here is the trick: You do not use the Windows 10 KMS key located under Windows 10 Enterprise product, but a separate one for Windows Server 2012 R2 named:
Windows Srv 2012 DataCtr/Std KMS for Windows 10
You will find that key by navigating from the License tab and then Relationship Summary
Then click on you active License ID and on the next page click on Product Keys.
Scroll down and you will find the key named Windows Srv 2012 DataCtr/Std KMS for Windows 10
3. On your KMS server, run an elevated PowerShell and enter:
slmgr /ipk <yourkey>
4. That’s it, your KMS server will now be able to active Windows 10 clients, as well as Windows 8.1 and Server 2012 R2.
To manually test an activation you can run:
slmgr /ato from an elevate PowerShell