Whenever we try to activate Windows Eval Directly using our Windows Retail or SPLA key (KMS or MAK) it will always throw an error as below ,
Error 1168
The specified product key could not be validated.
Check that the specified product key is valid and that it matches the target edition.
So while activating Eval Windows Editions we have to always use GVLK Keys to upgrade from EVAL to Full all Steps are mentioned below
How to Switch Windows Eval to Windows Generic then SPLA (Our Retail Activation)
1) Accept terms
DISM /online /Set-Edition:ServerDatacenter /GetEula:C:\eula.rtf
2) Check Current Edition
DISM /online /Get-CurrentEdition
3) Check Target Edition
DISM /online /Get-TargetEditions
4) Activate Microsoft Generic License First
a) DISM /online /Set-Edition:<edition ID> /ProductKey:XXXXX-XXXXX-XXXXX-XXXXX-XXXXX /AcceptEula
Use GVLK Keys from this link as per product edition
https://learn.microsoft.com/en-us/windows-server/get-started/kms-client-activation-keys
Example for Windows 2012 R2 STD
DISM /online /Set-Edition:ServerStandard /ProductKey:D2N9P-3P6X9-2R39C-
5) Then Activate using SPLA license
slmgr /ipk <–Product Key–>
OR
Just From My Computer Settings go to Activate Windows and enter your Key