when running the windows 10 upgrade downloaded from Microsofts site it does not ask for a new key and will get the message setup-has-failed-to-validate-the-product-key
https://superuser.com/questions/947130/windows-10-setup-has-failed-to-validate-the-product-key
None of the other answers worked for me, though Moshe Katz’s answer did point me to the log files. Under C:\$Windows.~BT\Sources\Panther there are two log files, including an setuperr.log which indicated to me that it was in fact a license key issue. This did cause me a little confusion because I was never prompted to enter a key; I suspect Setup was attempting to autoactivate using the Windows 7 key or was looking for a Windows 10 OEM license in the BIOS.
I opened an admin command prompt, browsed to C:\ESD\ where the media creation tool stores its files, and I ran setup /pkey xxxxx-xxxxx-xxxxx-xxxxx-xxxxx using the retail product key we purchased and Setup worked perfectly.