You are most likely an administrator of the Flexi system, but not of the server, as the main administrator has probably not granted you those rights.
We recommend finding out who in your system logs in under the username "admin" — that is, as the main administrator — and requesting from them the right to create users.
The main administrator can grant other users the right to create users as follows:
go to the menu Tools – Users in Company,
on the detail page of the user who needs to be able to add new users, open the Login Credentials tab and click the Server Rights button,
in the newly opened window, check the Create Users flag,
click the Save and Close button.