If you simply cannot pay, do not resort to piracy. Use open-source software that is just as powerful as Vegas Pro 12 was in 2012:
Pros:
If you actually own a legal license for Vegas Pro 12, here is how you should handle the authentication:
Finding a legal authentication code for Sony Vegas Pro 12 (64-bit)
: If you have a physical copy, the serial number is typically found on an activation card or a small slip of paper inside the box. Troubleshooting Activation Issues
Sony Vegas Pro 12 is a powerful video-editing tool, but some users hit an “authentication code” or licensing error when installing or launching the 64-bit version. This post explains likely causes and step-by-step fixes so you can get back to editing.
: You should be automatically prompted with an activation window upon startup. Enter Serial Number : Input your serial number (typically starts with Registration Options
Are you trying to of Vegas 12, or are you curious about how modern versions handle licensing?