“If after trying all of these advanced steps the activation still fails... you may have reached the limit of what is technically possible for reactivation. The most secure path forward would be to perform a clean installation of a supported operating system...” Microsoft Learn
If the standard GUI activation fails, follow these steps in an elevated Command Prompt (Right-click Command Prompt and select Run as Administrator WordPress.com Remove existing key slmgr.vbs -upk and press Enter to uninstall the current product key. Clear registry entries slmgr.vbs -cpky to clear any remaining key data from the registry. Install new key slmgr.vbs -ipk with your 25-digit code). Activate online slmgr.vbs -ato product key windows server 2008 r2 standard fix
If your server is failing to activate, you can try these standard administrative fixes: “If after trying all of these advanced steps
C. Convert from evaluation to licensed edition (if applicable) Clear registry entries slmgr