How do you redeem marvel machine items in the current cash shop?

Try the code again, sometimes it glitches up, coupons is most likey the correct option. If the problem persists, log a ticket.
Also do note again that the code cannot be used by any other accounts than the one that played the marvel machine.

Well, I've tried the code several times on both my accounts, to no avail, so I guess it's time to report. If anyone finds a solution, please quote or pm me so I see the notification.