Just wanted to confirm that you were indeed on the correct step. Some users were mistakingly on the third step still. Because you still have the quest on you, you should be able to go back into the raid and get it. Unfortunately you'll need to do all the puzzles again, or at least join at a boss checkpoint where the puzzles had been completed in that run. A couple of things to keep in mind: make sure to open that second chest (don't let the fireteam leader return you to orbit until you've done so), and leave room in your inventory for it (there's a glitch where the Divinity isn't going to the Postmaster, but it completes the quest and you can't get it again).