A postback request occurs between two servers, and is meant to tie conversion events happening in the Sending Server, with web or mobile engagements events happening on the receiving server. 1. The Sending server: A server where the conversion event takes place. Usually an affiliate network’s server, ecommerce platform, or merchant. 2. The receiving server: A server that can ingest the conversion data.   Whenever an event such as a purchase happens on the Sending Server,  the server will send a POST or GET request to the “postback URL” provided by the receiving server. Upon receiving the purchase event data, the server will send a response to the sending server to inform it that the data was received with or without errors.