How do I know when Apple gift card was redeemed

When you cannot redeem the Apple Gift Card or App Store & iTunes gift card.

Where to buy a physical Apple Gift Card or App Store & iTunes gift card: at an Apple Store or an Apple Authorized Reseller in your region.

See also:  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

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