Failed to create user after adding dn attribute

[wzbname]

• Adldap2 Version: v10.4.3
• LDAP Type: Active Directory
• PHP Version: 7.1.11

Description:

          $user                             = $provider->make()->user([
              'cn' => 'John Doe',
          ]);
           $user->save();  return true;
           
          $user                             = $provider->make()->user([
              'cn' => 'John Doe',
              'dn' => 'cn=John Doe,ou=Users,dc=gdcg,dc=cn'
          ]);
           $user->save();  return false;

I don't understand why after adding the attribute of dn, $user->save(); return false