Referrals are based on your Client ID.
You can generate a Client ID by creating a new App and enrolling it in the Uber Affiliate Program on the Developer Dashboard.
Be sure to use this ID for all API calls and Deep Links in order to ensure proper tracking of your referred users. In particular, for users that do not have the Uber app installed, play close attention to the Mobile Web Deep Linking guide.
You will be eligible for payment for each valid first trip in the U.S. by a new user whose trip request originated through your API integration or Deep Link.