When you receive this error while trying to import your Windows 10 product keys to KMS VAMT server 3.1, the only way is to upgrade your VAMT version.
It is not possible to import Windows 10 keys in VAMT 3.1 keys.
Download the software from Microsoft:
https://msdn.microsoft.com/en-us/windows/hardware/dn913721.aspx
Direct download :
http://go.microsoft.com/fwlink/p/?LinkId=526740
Installation:
Click Next
Click Next
Click Accept
Select VAMT & Microsoft SQL Server 2012 Express if you don’t have an SQL server installed., and click Install
And Wait
Click close
Add a Database name : VAMT
Click Yes
VAMT is now installed
VAMT is now version V10.0.10240.0
Select Product Key => Add Product Key => add your product key
Add your Product key
The product key is installed.