You may having some issue with the general documentation of activating Windows Server 2012 R2 with a product key.
Here I’m going to show you a easy method for activating the server in a minute.
First, make sure you have downloaded the standard evaluation version from Microsoft. If you have Core edition installed this method will not work. If not downloaded yet, search on Google for “download windows server 2012 r2 standard iso” and download the DVD Image ISO file from the official Microsoft site. When installing Windows Server 2012 R2 evaluation, choose the Standard edition with GUI selection. After you have the server installed in your machine, proceed to the activation process.
Let start with opening the Command Prompt window.
Check the current edition:
DISM /online /Get-CurrentEdition
The result should look like the evaluation edition ServerStandardEval
So, we should upgrade the Windows edition from Eval to Standard version. We will keep the ServerStandard portion only in to our activation command.
Buy a product key to get the server activated, and insert/replace your product key in the below command. You can use cheap ESD license or Volume license key as well.
DISM /online /Set-Edition:ServerStandard /ProductKey:XXXXX-XXXXX-XXXXX-XXXXX-XXXXX /AcceptEula
The server will be restarted and you are done.