This token exists to transmit dynamic cost values from your traffic source. In your campaign setting you can indicate statistical values and, if the dynamic values differ from previously given statistics, then the dynamic value will be chosen for counting statistics based on its relevance. This function is available for the CPV and CPM models (for CPM models, the cost for 1000 impressions will need to be transmitted in the link. This value will be divided by 1000, assigned to each impression).
Why is the Cost parameter needed?