Adding Windows 10 to your Server 2012 R2 KMS Server

1. Make sure you have the latest Hotfixes that allow Windows 10 KMS keys.  I got them using Windows Update, but you can also download them as hotfixes.

3086418 Error 0xC004F015 while activating Windows 10 Enterprise using Windows Server 2012 R2 KMS Host https://support.microsoft.com/kb/3086418

2. Go to the Volume License Service Center and see if you already have KMS keys.
If your using Server 2012 R2 (2008 R2 is not supported for Windows 10 KMS) you will need to get a KMS key called "Windows Srv 2012R2 DataCtr/Std KMS for Windows 10".

In VLSC - click License, then Relationship Summary.

Now click the License ID of your current Active license.

Once the page changes, click Product Keys.

Scroll down the list and look for "Windows Srv 2012R2 DataCtr/Std KMS for Windows 10"

 If you are missing the KMS keys from the MVLSC then you need to contact Microsoft at KMSADD@microsoft.com to get your MAK key converted to KMS.
You will need 2012R2 with SA to get this Special KMS key.
If you want to call them, use this number: (866) 230-0560
If that doesn't work for you, here is the page with all the other VLSC phone numbers:
http://www.microsoft.com/en-us/Licensing/existing-customer/activation-centers.aspx
Here is the format of my email to them:

------------  Start email Template  ------------

Hi,

I need this KMS key generated: "Windows Srv 2012R2 DataCtr/Std KMS for Windows 10"

Here is my Server 2012 R2 DataCtr/Std with SA License agreement:

License ID: XXX

Parent Program: XXX

-- (Note: The Win10 License may not be required, but I included it in my mail anyway) ---

Here is my Windows 10 Enterprise License agreement:

License ID: XXX

Parent Program: XXX

------------  End email Template  ------------

3. Open up an Elevated Command Prompt window and change to the C:\windows\system32 folder.4. Use this command to add your KMS key to your existing KMS Server:
    slmgr.vbs /ipk XXXXX-XXXXX-XXXXX-XXXXX-XXXXX

5. If you have an existing Windows 10 Enterprise installs that you need to point to the new KMS server, use these commands: (The key is not my KMS key, it's the generic key used to tell the client to look for your KMS Server)
  slmgr.vbs /ipk NPPR9-FWDCX-D2C8J-H872K-2YT43
  slmgr.vbs /ato

Reference: https://technet.microsoft.com/en-us/jj612867.aspx

6.  Now check your KMS status
     slmgr.vbs /dlv

Other useful tips, sites and error codes:
Force a PC to go get a KMS License from a server you choose manually:
slmgr.vbs /skms kms.mydomain.local

When I tried to enter the stand alone Windows 10 Enterprise KMS key on a Server 2012 R2 KMS Server that was already setup with the Server 2012 R2 Datacenter KMS key, I got this error:

Error: 0xC004F015 On a computer running Microsoft Windows non-core edition, run
'slui.exe 0x2a 0xC004F015' to display the error text.

This was because I didn't use the "Windows Srv 2012R2 DataCtr/Std KMS for Windows 10" KMS key.

KMS Activation rules:
Datacenter Key can activate Datacenter, Standard, Client versions of Windows
Standard Key can activate Standard, Client versions of Windows
Client key can activate client versions of Windows.

This information was compiled by many pages of information, here are a few good ones:
http://www.techcheez.com/windows-10-kms-activation/
https://www.reddit.com/r/sysadmin/comments/3fh9gv/steps_for_windows_10_kms_activation_against_2012r2/
https://social.technet.microsoft.com/Forums/en-US/666b8ac6-d39d-43a1-abc5-e7cd9489accc/windows-10-kms-requirements?forum=win10itprogeneral