On getting rid of a Win 10 Pro license

Hi all,

I erroneously purchased a Windows 10 Pro OS license which I cannot use (I was supposed to purchase a straight-upgrade from Win 10 Home). I'm willing to take a small bath and sell it for $100 (I paid $140) just because I seriously can't use it.

So a question I have is: What's the least irritating way for me to try to sell this thing? I'm sure some of you younger, hipper techies deal with this stuff so I'll defer to you. My main thing is that the DVD is open already, though the key is completely unclaimed.

Thanks for your attention.

Post in the buy and sell thread.