I’ve got 15 work laptops that needed to be upgraded to Windows 10, all are eligible for the free upgrade but some of them refused to upgrade via the ISO method saying the setup couldn’t verify the license key.
At first I suspected that the setup was throwing the error because the update wasn’t reserved, when I tried to reserve the update I couldn’t find the Reserve button.
This turned out to be a easy fix, ran windows updates to find there were a couple of updates available, installed those and re-ran the installer and voila! The setup started and upgraded the machine.
So if you come across a similar update, making sure the machine you’re trying to upgrade is fully updated.