Go into MyTEAM, sit on the Buy Packs screen for more than 30 minutes.
Don't do anything. You'll get put into a "Black Market" window after you back out of the menu 30+ minutes later.
At the time of writing this, I'm not sure if the Black Market goes away, so I recommend if you actually are playing MyTEAM, to go in with a bunch of credits, some of the card deals in there are excellent.