Follow these steps to get a free steam key for dlc Cryptographer's Colour for Payday 2 (will prob appear in game with the next dlc update)
https://www.reddit.com/r/paydaytheheist/comments/hbh3hr/the_complete_guide_to_cartographers_colour/
its a bunch of online puzzles all of which have already been solved. you'll get the key on the last screen like below. There's a chance of duplicate keys so if you get an error saying the key has already been activated, refresh the locke breacher page. Happened to me and I didn't have to do the puzzles again, you just go Arsenal Upgrade again and it should generate a new key.
Edited