When trying to activate Server 2019, you may get this error:
The product key you entered didn’t work. Check the product key and try again, or enter a different one. (0x80070490)
This isn’t Windows Server 2019 Activation problem, it’s just a bug entering the product key.
To workaround this bug and activate windows, open a command prompt window in elevated mode (right click -> Run as Administrator) and enter the following command with your product key instead of the XXX’s: