cPA model: Cost per Action(CPA) model is useful when an advertiser wants to pay only for some action of the banner visitor. It can be a sale or a sign up to a newsletter or trial offer, thus a conversion is needed for the advertiser.
According to the following example, the advertiser will pay $3 for the each occurrence of the action. The maximum number of Conversions is 1,000. So, the publisher can earn up to $3,000. Notice that we have defined a maximum value for the Clicks option. It means that the campaign will end regardless of the remaining conversions in the inventory if the Clicks number reaches 50,000. The other case
is also valid. If the campaign gets 1,000 conversions, the campaign will deactivate automatically regardless of how many clicks are left.