NOTE: I have not played the Steam version of this game, but I'll go ahead and post the solution I put on TrueAchievements for your convenience. For clarification, I played the Windows 10 version of this game on Xbox and I'm sure it isn't too different from the steam version.
In order to unlock this achievement, you need to download a program called Professor Helper. I recommend going for this achievement after completing first two cases of the game.
If you search for "software" in Hypnospace Explorer you should find a webpage called "Professor Helper for HypnOS". Simply click on the link and then click "Click here to download and install Professor Helper for HypnOS". it will download a file called professorhelper. Double click on the file in your download manger and the program will install. After it installs the achievement should unlock.
*** Spoiler - click to reveal *** Now what you have Professor Helper installed, he will be very beneficial with your Capa Cash case, as all of his advertisement links that will pop up will bring you to a page accepting Capa Cash. Whenever he pops up, click yes and then click to go to the web page. you should see four different advertisements pop up while professor helper is installed on the system. Each of those pages includes an image saying "Buy now with Capa Cash". Report all images with Offence 5 E: Extralegal Commerce and you will have enough to close the case.
Just a few extra notes here:
-You can visit all of the ad links directly by searching for ProfessorHelper in Hypnospace explorer and by clicking on the "Professor Helper Ad Director".
-When you click on the ad promoting the "Free Cruise and Credit Report" in the ad director (or the ad that tells you you won a free cruise while clicking yes to the Professor Helper pop-ops) you will be infected with the "WaveHello" virus. If you have HypnoCure installed, be sure to click on "cure me" to get rid of the virus, otherwise you'll constantly see you screen rock back and forth and hear waves in the backround.
As time goes on, I found Professor Helper to be more and more annoying than helpful. Unfortunately, it's not easy to uninstall. if you try to drag the professor icon to the recycle bin it will tell you that it needs an uninstall program in order to remove a program from your desktop. At this point, launch Hypnospace Explorer, and search for "uninstall". You should see one link pop up called "Professor Helper Uninstall". Click on it, and you will need to pay 33 hypnocoins in order to remove him. Once the fee has been paid, the professor is gone, until you choose to install him again.