Brother please make it free because many people just are better off spending 2 euros on other things than some paid mods which they probably use one or two times.
Have you looked at the bottom of the car list, it may be listed as props (like the Agent simplified traffic cars)
Have you extracted the zip file before dropping it to the mod folder? It has 2 seperate mods, mobile and stationary versions as zip files so it doesn't work if you don't unpack it. If you have, please try with other mods disabled. --- Post updated --- Alternatively you can drop the 2 zip files to mods folder after unpacking the file instead.
what I might say may sound extremely bias, but I like to blame this on the rise of paid mods in general. Many people saw that big mod creators were putting their mods behind a paywall and others decided to follow suit because they thought it was a fair idea to get contribution after hours of work on a mod. While I get modding takes a long time, What I don't get is how there has been a rise in many people who have decided to make a whole lot of mods behind a paywall, especially those that are either low quality or don't offer as much as a high quality mod would.