Clicks
This refers to the number of times your referral link has been clicked. A click will be recorded regardless of whether the person signs up or not. These are not unique, so one person can generate many clicks.
Sign ups
Refers to the number of people who have used your code and completed the sign-up process. This could lower than clicks, and it might include people who still haven't earned you a credit.
Earned
Refers to the amount of credit you have accumulated. Credit is applied after your referrals have paid their first invoice.
