CPA (Cost Per Acquisition) is the model where the operator pays a fixed amount per acquired player meeting a criterion, in iGaming, almost always an FTD above a minimum value, sometimes with an activity requirement.
The risk sits with the operator: it pays upfront and finds out later whether the cohort had value. For the affiliate, the advantage is predictable cash flow.
What decides whether the deal works is the qualification criterion. A CPA triggering on a minimum deposit produces exactly minimum-deposit traffic. Two-trigger criteria, value above a floor plus activity in a second session within a window, usually reduce FTD volume and improve the cohort enough to more than compensate.
Also relevant: attribution window, treatment of players touched by more than one affiliate, payment terms, and whether the affiliate can audit its own numbers.