This is most often the case of digital fingerprinting; the client will often have this enabled as part of their survey tool.
This service is intended to stop duplication or those attempting to do the survey more than once. So if a person is a member of multiple survey companies they will likely get redirected as a "Duplicate" or "QA flagged" if they have already been identified as having attempted the survey.
It will also do IP address validation, so it'll check your location to make sure you are accessing from the right country.
This process is not 100% accurate, so if you are repeatedly flagged as a Duplicate and you are not a member of other survey providers, please email use at firstname.lastname@example.org and we’ll investigate.
As we don't write the surveys, members of other survey providers will be invited via others first. If you are a member of other survey providers/groups then this will limit your opportunity to earn the highest incentive for the exact same survey.