When a user is not eligible for a survey we fire instantly within the SDK or WebPlugin the UserNotEligible notification. The Publisher does not have to wait for a server-to-server callback since he can rely on the local notification he has already received within the SDK or WebPlugin (so no validation is needed from the Pollfish server side in that case). Having said that, a Publisher can inform the user instantly that he was not eligible for that survey.
Example (from a partner integration):
If a user answers all questions in a survey and the local notification SurveyCompleted is fired within the SDK or WebPlugin, then, that survey response will be sent to the Pollfish server side for validation. This means that in that case the publisher should register and wait for the Pollfish servers to send a callback prior torewarding or informing the user on the success or failure of the survey completion. Our Pollfish servers will then fire a callback to the publisher informing him if the survey was completed successfully or if the user was not eligible (the publisher has to enable this through the settings in the s2s section - point 6).
If our servers inform the publisher that the survey was completed successfully, then the publisher can award the user since the survey revenue will be definitely credited to his account. If the s2s fires a user not eligible event, that means that the survey responses from the user did not pass our validation checks and it was either marked as fraud (which can mean a lot of things like hasty answers, straight lining, gibberish, answering too fast etc.) or the user was simply not eligible for that specific survey.
All these logs can be found on the Developer's Dashboard, too.