You created media and performed a clean installation of Windows 10, instead of first upgrading from your previous version of Windows
In order to upgrade to Windows 10 using the ISO image or upgrade media you created using the media creation tool, you need to select the Upgrade this PC now option.
If you performed a clean installation instead of an upgrade, you'll be asked to enter a Windows 10 product key or buy a new license in order to activate Windows 10. This is because we weren't able to register your free upgrade entitlement with the activation servers because you didn't upgrade to Windows 10. To fix this, you'll need to go back to your previous version of Windows, make sure the previous version is activated, and then upgrade to Windows 10.