What is CPA (cost per action)?
The action is set by the merchant: a first deposit, a paid trial, an app install with registration or a completed purchase. The amount stays the same no matter how much the customer spends later.
CPA is simple to compare and pays relatively early, which is why it dominates paid traffic. The catch is in the details: minimum deposits, qualification rules and daily caps can make a high CPA earn less per click than a lower one.
Example: an offer pays $60 per first deposit of at least $20. A deposit of $15 earns nothing; a deposit of $500 still earns $60.