I want to send data from a particular sites/customers

callstats.io offers setting a SiteID for each person in a call. You can further filter by SiteIDs on the dashboard. 

SiteID can be set in configParams

var configParams = {
  disableBeforeUnloadHandler: true, // disables callstats.js's window.onbeforeunload parameter.
  applicationVersion: "app_version", // Application version specified by the developer.
  disablePrecalltest: true // disables the pre-call test, it is enabled by default.
  siteID: "siteID", // The name/ID of the site/campus from where the call/pre-call test is made.
};

Alternatively, if you want to keep each customer data separately for privacy reasons, for example support teams or admins should be able to see certain customers and not all -- callstats.io's role based access is not supported for siteIDs. In this case, you may consider creating an appID for each distinct customer, everything sent to a particular appID is aggregated under that umbrella. if you have distinct customers that cannot be distinguished by a ConferenceID or userID, then we suggest assigning each customer a separate AppID.