The amount an affiliate gets paid every time a visitor referred from an affiliate makes a purchase. This form of advertising is based on a transaction rather than impressions or clicks. CPA is used widely in affiliate marketing (also known as multi-level marketing). CPA can be proportional to the value of the client's purchase or a set amount. MyNewsletterBuilder (MNB) provides Enterprise Accounts allowing the main advertiser to track the click-through rates (CTR) of their affiliates' newsletter campaigns.