In most cases, incentive sites grant rewards for completing requirements. This usually requires viewing advertisements, signing up for a site, entering a PIN code (through a mobile device), purchasing trial products or full products or completing surveys. This in turn rewards the specified user in cash, points, check, or its equivalent. Alternately, an offer may entail referring website visitors by inviting them to a target site under a referral link (unique to every user). Referrers in turn are either paid for every person they invited or as percentage of resulting revenue.