With pixel URLs becoming more unreliable, as they have a lot of performance issues, and sometimes it just don’t work. Postback URLs came out as a solution to this situation also most advertisers use postback protocol for tracking as it is more detailed. Postback URL or server-to-server communication, communicate between third-party tracking tools such as Redtrack, Clickmagick, etc. It can also be an affiliate network like Maxbounty, Peerfly, clickbank, etc.
As these tracking tools are quite accurate and also store data, that is the reason for them to charge you for their services.
Use of Postback URL
With postback URL you can insure the clicks and keeps track of them.
Type of postback urls
There are two types of server postback tracking, one postback tracking with transaction ID and other postback tracking with affiliate ID.
When an affiliate network generates a sale, it communicates with the third-party tracking tool via postback URL, and it sends the sales data back to the network and allows a third-party tracking tool to track it.

A postback URL is given to your affiliate network and what that affiliate network does is that it use it to send the sale that has come up on your account, and that’s how this postback URL works as you have this tracking tool, you get a click, you get a sale, and you give the URL to this affiliate network and the affiliate network gives the sale back to that third-party tracking tool.
How affiliate networks map the URL with user
Affiliate network use click ID which is generally in a number depending on the people connected to network. As you generate your click number you get a click ID which is like a ticket based on the total users of the page then this click ID is passed through from one tracking link via this click ID through all the pages till it reaches the final sales page then that affiliate network sends a ping back to the URL from clickbank, etc.
All the click IDs must be unique to log conversions, and duplicate conversions are automatically rejected. As in the case of advertising, advertisers have to face huge loss and wreck the trust with host.
This helps to prevent fraudulent traffic, server issues, or other human interference from affecting report data and presenting erroneous statistics.