How does Amazon Rekognition Liveness charges users? Per successful or unsuccessful attempt or both?

Hi,

How does Amazon Rekognition Liveness charges users? Per successful or unsuccessful attempt or both?

Let's take the following example: I have a platform (website) where advertisers comes to get real views to their websites, and where promoters comes to find advertising campaigns in order to promote them. The advertisers are paying for views, and the promoters are paid also for views. Each promoter gets an unique link to each of the campaigns in order to promote it. Each link has Amazon Rekognition Liveness to it in order to scan each visitor that might arrive there. What happens if some promoters are using bot traffic/spam traffic and it is automated in a way that just allows the camera to be accessed, and then they DO NOT pass the liveness check? What happens at this point? Is the user (my platform) charged per this attempt that was unsuccessful? Or the user is only charged by successful attempt? I'm asking this as some promoters might spam their own unique links and bring 100.000 spam/bot visits each day to their links and all of them might result in an unsuccessful attempt. At this point out platform would have to pay for all of these users that came here and did not passed the Rekognition Faceless test. They could spam us and we would have to pay tens of thousands per day for all this spam traffic.