In case you are getting error 801c0003 (This user is not autherized to enroll) when joining your computer to Azure Active Directory, it is likely that you need to modify the default device settings in Azure AD. Log on to https://portal.azure.com, go to Azure Active Directory->Devices and check the device settings, in particular the options Users may join devices and maximal number of devices.
…the settings to fix it…
…and the message that makes us happy.
Great articles in this context:
Michael Niehaus, https://blogs.technet.microsoft.com/mniehaus/2018/01/19/afraid-of-windows-10-with-azure-ad-join-try-it-out-part-1/
Sander Berkouver, https://dirteam.com/sander/2018/03/20/knowledgebase-you-receive-error-801c0003-when-you-try-to-azure-ad-join-a-device-during-the-out-of-the-box-experience-oobe/