Windows Server 2019: Error 0x80070490 When Activating Windows

After installing Windows Server 2019 Standard, I tried to activate it with a MAK key from the Microsoft Volume Licensing Portal. I clicked on "Change product key" and entered the key from the Microsoft Portal. I got the following error message: The product key you entered didn't work. Check the product key and try again, or enter a different one. (0x80070490) Searching on Google, this error number mostly refers to Windows Update or Windows Store errors, but not to licensing issues. I finally Read more [...]