The principal user name exists in Azure AD; the issue comes when adding the user account to the analysis services. As per the message below ( I have substituted the real user name, surname and domain name ), I can see that the apostrophe causes the issue.
Failed to save modifications to the server. Error returned: 'The user or application: '<pii>UserName.O'UserSurname@Somedomain.org.au</pii>' was not found in your organization's Azure Active Directory. Details: '<pii>The remote server returned an error: (400) Bad Request.</pii>'.
The interesting thing is that this did not happen a few days back. I mean to say that the user has been accessing the service with no issues until recently.
How do I add a user with an apostrophe in their name as a member of azure analysts services?