Configuring LDAP settings in Account Details – LDAP Authentication page, can see success message when saving the domain controller info but while importing users it fails.
Issue in mapping the sAMAccountName from AD. So we are not getting login for the users thus failing the import.
Only in Pre Windows 2000 version we map the sAMAccountName for login name and after that we use the userPrincipalName attribute. So please select LDAP Server Type as others and in Login Attribute Label type userPrincipalName and then try to import. Refer image below.