Each site has a different site ID which allows us to identify each site. These are created after a site has been submitted for approval and can be found within the Partner Portal Site Details section.
To locate the site ID for each of your sites, navigate to the Partner Portal and view the Dashboard tab. Here you will see a list of your live sites. Click into the site and expand the Site Details section, and the ID is the located at the top left.
This will be a four or five digit number.