Lexis Create DMS needs the user principal name to create new users to ensure the proper and secure working of the Single Sign On solution. In most organisations, both user principal name and email address are the same. See screenshot of Azure AD user management
Please check and let us know if a user principal name is not the same as the email address. In this case, we will need a list of User Principal names to create the new users.
Click to see an example screenshot
https://lists.office.com/Images/9274ee3f-9425-4109-a27f-9fb15c10675d/4e76f2e8-133a-4cc3-86a8-d4ede881a9b9/T55BE4FNW61VG36UD4VP1EV39L/505b1a47-90df-473c-82be-553fb11f2743