When attempting to activate Windows Server 2019 after installation is already complete generates the error code “0x80070490: The product key you entered didn’t work”.
Solution 1 (Bad)
Reinstall Windows and input the license code during installation
Solution 2 (Good)
Activate Windows using the command-line. The error seems to be limited to the GUI.
c:\Windows\System32\slmgr.vbs /ipk [LICENSE_MAK_KEY]