Gift card redeem

How to redeem your Apple Gift Card or App Store & iTunes gift card

https://support.apple.com/en-us/HT201209

OR

Seems there are a few different apple gift cards.

To find out which one you have, 

and what you can do with it, 

Apple has a support page (link below) to help.

https://support.apple.com/en-au/HT204199

See the article below for what payment methods you can use in your country or region:

https://support.apple.com/en-au/HT202631

And

If your card works with your Apple ID:

What you can buy with your Apple ID balance:

https://support.apple.com/en-au/HT211187

Or

How to add money to your Apple ID balance

https://support.apple.com/en-us/HT201209

All the best :-)

Wondering which gift card you have,

and

which method(s) you tried without success,

and

whether or not you are getting an error message

___________________________________________________________

See if this helps:

First:  See what payment methods are available in your country or region

Payment methods that you can use with your Apple ID:

  https://support.apple.com/en-au/HT202631.

Second: If you know you can use gift cards as a payment method,

Try adding the Gift Card to your Apple ID account.

Change, Add or Remove Apple ID Payment methods

https://support.apple.com/en-us/HT201266

If you need more help, try Apple Support:

There is a "Get Support" link to Apple at top right on this discussion page

OR

See a list of Apple phone numbers around the world:

https://support.apple.com/en-us/HT201232

All the best :-)