Postback is used to pass the information like conversions, app_events, sales, leads captured to the publisher. It can either be at the Global level or Campaign level to pass the necessary information. 

Follow these general steps to add a publisher's postback-

1- Find the Postback/Pixels tab in the left section of the panel under the publisher's tab.

2-Go to the "Action" button and click on "New Postback" option

3-Enter the necessary details including the URL and update Trackier's macros adjacent to the respective publisher postbav parameters. Hit the 'Add' button at the bottom of the page after the required details are filled.

To know more about it please Click Here