When I redeem a card like today I had a 40 dollar iTunes card and I only got 18 :(

First of all, try restarting iTunes on your device to see if your balance simply hasn't been updated.

Second, make sure that you have followed the proper redemption procedure for each card as given here: Redeem App Store & iTunes Gift Cards, Apple Music Gift Cards, and content codes - Apple Support

If the code on the card was already exposed, then the balance on the card may already have been redeemed.

Third, if the previous steps did not solve your issue, read through this article and try the solutions listed there: If you can't redeem your App Store & iTunes Gift Card, Apple Music Gift Card, or content code - Apple Support

If none of the above works, contact Apple Support: Contact Apple Support

Log out and back in. If the balance doesn’t correctly update, click here and contact the iTunes Store staff.

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