NHL 24

This isn't quite as simple as it sounds. In order to buy or sell from the Auction House, first you have to unlock it. In order to unlock it you must complete all the Training Camp objectives under the Objectives Tab on the Main Menu of Ultimate Team.

They are:

• Win three games of Rivals, HUT Champions, or Squad Battles. Squad Battles is the easiest, as you can do it against the CPU on Rookie difficulty
• Win one game of HUT Rush, which again can be done on Rookie difficulty against the CPU
• Complete three HUT Moments. Also very easy as the Training Camp Moments count towards this

Once all three are completed you'll get a pop up saying the Auction House has been unlocked. From here you just have to buy or sell any kind of card, HOWEVER no achievement will pop.

You then have to exit out of Ultimate Team and re-enter, upon which the achievement will finally unlock.