"Resolution
Make sure you've entered the code exactly as it appears on your card. If the code is illegible, try to enter the code as best as you can. Invalid code messages typically mean that the card activation number may have been mistyped. Please read your code carefully. The following letters and numbers can look very similar:
The letter A and the letter H
The letter B and the number 8
The letter D and the number 0
The letter E and the number 3
The letter G and the number 6
The letter H and the letter W
The letter J and the number 1
The letter M and the letter N
The letter O and the number 0
The letter P and the letter F
The letter Q and the letter O
The letter Q and the number 0
The letter S and the number 5
The letter S and the number 8
The letter V and the letter U
The letter Z and the number 2
If you're still unable to redeem your code after verifying the characters in the code, you'll need to contact iTunes Store Support for help. You'll need to provide the activation code and serial number from the back of your iTunes Gift Card."