Server-to-server affiliate tracking requires affiliate tracking software such as Scaleo. This type of tracking is also known as "cookieless tracking" because it is not dependent on cookies and does not require anything to be installed on the user's computer to store information. Instead, the information linked to the user and the affiliate is saved on the merchant's server with a unique identifier known as the transaction ID. So, when a user completes a conversion after clicking on a unique tracking link, the system sends a postback to the conversion tracking system along with the transaction ID.