It'll tell you when you get on universalredeem.com and enter the code.
I've been able to redeem these codes by going on Vudu to the redeem tab even though it says to go to a different site. However that was a couple months ago so I am not sure if the codes can still he entered on Vudu directly but it would be worth a shot. Something I've seen is the Movies Anywhere app which is apparently an app that covers vudu and other retailers but I haven't researched it much.