If your build shows and will not accept a standard Retail or MAK key, you may need to convert the edition first using the Deployment Image Servicing and Management (DISM) tool:
This report covers product key types, activation methods, troubleshooting steps, licensing considerations, and recommended best practices for activating Windows Server 2012 R2 Standard (build 9600). If your build shows and will not accept
Not all keys are created equal. To activate , you need the correct key type: If your build shows and will not accept
– If you own Windows Server 2019 or 2022 licenses, you have legal downgrade rights to 2012 R2. Use the appropriate VL media and your newer license key. If your build shows and will not accept