Why isn't Windows activated?

I purchased Parallels Desktop 13 to install Windows 10 on my Mac laptop (High Sierra). I went to parallels.com/welcome, entered the product key I was given from the Parallels package in the mail, downloaded Parallels and entered my new Windows account. But then I clicked on the Windows logo>settings, and received a message that Windows isn't activated. I clicked the troubleshoot button. Then another message comes up. "Windows can't be activated on this device because you do not have a valid product key." But I already entered a product key when I installed Parallels. Do I need a 2nd product key for Windows?