Below is an overview of how the current licensing system works and why you don't need a traditional serial number anymore. 1. The Death of Serial Numbers
Instead of a serial number, the software is activated by logging into your VirtualDJ account directly within the application.
Since the software has moved to a subscription and account-linked model, here is how you can get "Pro" features today: Price and Licenses - VirtualDJ
The era of typing in long strings of characters is over for VirtualDJ.
Old versions like v5.7 were deprecated in 2014. Most modern licenses (Home or Pro) are designed for VirtualDJ 8 and newer. 2. Modern Licensing Options