This code has already been redeemed

I'm receiving a message that shows the redemption code has already been used, but no download occured. any help?

I've seen this happen before when the App Store is bogged down a bit. (Gosh, I wonder why that could be happening today...) My solution would be to quit the App Store, restart, then go to the "Purchases" tab and see if you have "OS X 10.11 Developer Beta" at the top of your list. If so, you should be able to start the download.

The code redemption won't work on 10.10.4 betas. Make sure you do it on stable OS X releases.

Redemption code worked for me on 10.10.4 beta.. like butter.

As with Calvin, I was able to redeem on 10.10.4 without issue.