Redeem gift card thru email

I tried to redeem a gift card in the App Store on my iPad and I entered the code the box grayed out for a second but came bacc noting happened. My husband tried to redeem it on his iPad under his account and it worked. He then sent me a gift card try an email, I opened the email, clicked on the redeem button, my apple account came up and went to the redeem page and it still did not work. It did the same thing again as before. I tried signing out and back in but it still does not work. Any ideas?