I need to purchase a gift card

1.

App Store & iTunes gift card -> Apple Gift Card - Apple (UK)

• Add money to your Apple Account balance anytime, no gift card needed.

2.

Where to buy a physical Apple Gift Card or App Store & iTunes gift card:

Actually, you can buy an Apple gift card at many places, it depends of course on where you live.

At an Apple Store or an Apple Authorized Reseller in your region certainly, but also at a good bookstore, supermarket and/or drugstore.

See also ⤵️

See this Apple article:  If you can't redeem your Apple Gift Card or App Store & iTunes Gift Card

If you can't redeem your Apple Gift Card or App Store & iTunes Gift Card - Apple Support

• You can't redeem Apple Gift Cards or App Store & iTunes Gift Cards outside the country or region of purchase. For example, if you bought an App Store & iTunes Gift Card in France, you can't redeem it in the App Store in the United States.

About Gift Card Scams -> About Gift Card Scams - Official Apple Support