Hi all. Sorry if I am being a total noob, but I have just been getting into this game.

Under the customization tab there is a background that says 'Background available at Operation 1'. The thing is, it's still locked even though I have done all the Operation 1 challenges, even going so far as replaying until I earned all three shards on every one.

What do I need to do to unlock this background? Thanks in advance.