Activate Win10 Enterprise with Upgrade Key

I have a valid lot of upgrade licenses for Windows 10 Enterprise, but the activation agent won't accept it. How do I make it accept it?

I also have valid lot licenses for WinXP Pro Install and Win7 Pro Upgrade.

However, I can't install those OSs -- XP doesn't install on modern hardware, and even when it does it needs software updates before it can install Win7. Then there's the fact that it's just not reasonable to install three OSs to get to the OS I need to run.

I installed Win10 Enterprise 64bit from the "trial" ISO image on Microsoft's website (version 1703, which is the version listed on my license).

However, when I go to activate it, it rejects my Win10 key (0xC004F050). I tried entering my Win7 key to see if that would make it ask for the upgrade key or something, and it gave me another error (0xC004F210).

How do I make it accept my key?