Read the link I posted here again:
[quote]
An issue has been identified with Hybrid Azure AD joined devices that have enabled multi-factor authentication (MFA). If a user signs into a device using their Active Directory account and MFA is enabled, the device will not successfully upgrade to their Windows Enterprise subscription.
[/quote]
If you're running Win10 1809, you'll have to install KB4497934. If you use later Win10 versions, this is already included.
For Win10 1803 or before, you'll have to temporarily disable MFA during the 30-day polling period for activation and renewal.