When an ArcGIS Online Organization Administrator attempts to delete a member from the organization, the following error appears:
Error: Unable to delete member <username>. Multifactor authentication support for the organization requires that you maintain at least two Administrators.
The member is a Designated Administrator for multifactor authentication, and cannot be deleted if deleting leaves less than two Designated Administrators in the Organization.
Remove the member as a Designated Administrator for multifactor authentication before deleting. The steps below describe how to remove a Designated Administrator in ArcGIS Online.
Note: An organization is required to have at least two Designated Administrators for multifactor authentication. If removing a member as a Designated Administrator leaves the organization with less than two Designated Administrators, ensure there is a replacement for the removed member. A Designated Administrator can be added by clicking a name on the Administrators list.