how i use my apple iOS giftcard with War Robots?

Redeem it on iTunes Store ( see screenshot) then your purchase on War Robots will be deducted from that redeemed amount .

I looked for this on various websites including youtube and solved it using to redeem an Apple Gift Card on your iPhone, follow these steps:-

1. Open the App Store or iTunes Store:-

 -For the App Store, open the "App Store" app on your iPhone.
 -For the iTunes Store, open the "iTunes Store" app.
2. Navigate to the App Store or iTunes Store:-

 -If you are in the App Store, tap on your profile picture in the top right corner.
 -If you are in the iTunes Store, scroll down to the bottom of the screen.
3. Tap on "Redeem Gift Card or Code":-

 -In the App Store, tap on your profile picture, then select "Redeem Gift Card or Code."
 -In the iTunes Store, you'll find the "Redeem" option at the bottom of the screen.
4. Enter the Gift Card Code:-

 -Scratch off the label on the back of your physical gift card to reveal the 16-digit code.
 -If you have an electronic gift card, the code may be emailed to you.
5. Tap "You can also enter your code manually":-

 -If you are prompted to scan the code and prefer to enter it manually, tap on the option to do so.
6. Enter the Gift Card Code:-

 -Type in the 16-digit code and tap "Redeem" in the top right corner.
7. Confirm the Redemption:-

 -Confirm the redemption by tapping "Redeem" again.
8. Balance is Added:-

 -The gift card amount will be added to your Apple ID balance.
Now, you can use this balance to make purchases in the App Store, iTunes Store, or other Apple services. The redeemed amount will be used for future purchases until it is depleted. Keep in mind that your Apple ID balance can be used for various Apple services, including apps, music, movies, iCloud storage, and more.