I thought that when I purchased Zorin 15 pro, I thought upgrading (as opposed to updating) was free because I actually purchased the free version?
look, $39 is not a big deal but it is just what I inferred from the wording.
The word "upgrade" has many uses ... and is over-used.
This can easily create confusion.
For example, you can open a terminal now and enter in:
sudo apt full-upgrade
which will fully upgrade all of your packages... But it will not upgrade the operating system to a New Release.
To add to the vague wording, Microsoft Windows began offering "Free Upgrades to Windows 'X'." They are not really free - and they make money in a myriad of other ways as a multi-billion dollar corporation.
As covered in the other thread; Choosing Zorin OS Ultimate (Now, Pro) is not purchasing a license but a single Product under the Brand name of Zorin OS.
The upside of it is not having to worry about how the company is making its money if you did not see a receipt...