Since your own topic says, 'new build,' I presume that means just that - a new machine.
No so with Windows 10, whether the license was obtained via upgrade or not. If it was Windows 7, whether way back when it was new or now, you'd need the license key any time you reinstalled, even on the same hardware. You just skip entering it when you're reinstalling and it will be fetched from Microsoft's servers. Windows 10 licenses are directly linked to the motherboard in a machine and once a machine has had a Windows 10 license activated on it you can install Linux, Windows 7, name your alternate OS and then go back to Windows 10 any time you like without needing a license key at all.
I don't understand what the issue is, unless you're trying to re-use an old Windows 7 retail license to install Windows 10 on a different machine than the original Win7 and Win10 upgrade from it ran on.
