Q: Why am I being asked for credit card info when trying to use gift card?

If this is happening in the US store it is because the gift doesn't cover the full amount of the purchase. the US store prices do not include the local sales tax that is added on in the final steps of the sale. You will need to redeem another gift card and increase your account's available credit or supply a credit card to complete this sale.

You need to take into consideration any applicable taxes and or fees added to the purchase price mentioned here > iTUNES STORE - MAC APP STORE - TERMS AND CONDITIONS

You can select None for payment method >  iTunes Store: Changing account information

The system automatically uses a credit balance on an account first. It would only ask for another form of payment if the credit on the account was not enough to cover the total.

You may be running into this as a security measure as the system is trying to determine that you are the rightful user of thhe account. You can follow this user's instructions to go into your account using the iTunes app on your Mac or PC and choose the None option in the payment methods.

This user, mountaingoatgirl, explains how to get a None option in your account details in the iTunes app on a Mac or PC. -

https://discussions.apple.com/message/24907941

Should you continue to have issues contact the account security team;

Apple ID security issues -

Call Apple Care and ask for the Account Security Team. They can assist you with your issue.

http://support.apple.com/kb/HT5699

i have 15$ in my apple account and all im buying is a 99 cent game, but when i send buy(sending the app as a gift) it asks me to add credit card info which i dont have