The first vending you run into is in the Medical Pavilion. Turn left and it is next to a security bot blocking the door. It does not give you the option to hack the vending machine right away so you must hack the security bot first by pressing
. This gives you a tutorial on how hacking works in this game. Once you completed hacking the bot you can move on to the vending machine and do the same thing. When you finish all the prices become discounted and your achievement should unlock.
*IMPORTANT If you did not get your achievement right here, check the progress tracker. If there is no progress for that or any of your audio diaries collected, start a new game. The game might glitch for some people. I have hacked several bots, cameras & vending machines but nothing unlocked or made progress. It was at this point I started a new game, got to here and it unlocked right away.