I want to add a few new fields at the registration from for different sites.
for example:
Site A will have country and city fields
Site B only add on country field.

I added a few lines code at the registration form as following require_once(JPATH_ADMINISTRATOR.DS.'components'.DS.'com_multisites'.DS.'classes'.DS.'utils.php');
$session =& JFactory::getSession();
$site_id=$session->get('site_id', null,'contracts');
echo $site_id;

I got no return value of $site_id

Any idea of how to get the value of $site_id?
Thank you,
Amy Foy

First condition to have the script executed, is that you have the "billable website" functionality enabled when you define the "mutlsites" menu entry.
Only billable website can execute scripts or plugins.

The second condition is to process the "billable website" functionality is that you have website quota avaialble.
You can order such quota when you go in the "settings" menu.

where is the "setting menu" ?

In JMS, you have
- Manage Site
- Template
- Check patches
- User manual
- Check for update
- SETTINGS <--------------- HERE
- About us