Did not receive apple gift card

Hi alyaa276.

welcome to the Apple (user-to-user) Community.

Re: "Did not receive apple gift card" : "for the first time i didn’t receive the email! I don’t know what to do"

Wondering if you purchased the gift card from Apple:

If you purchased the gift card from Apple as if it was for yourself:

See Apple Support's article: Check your gift card balance - Apple Support

If needed:

Call Apple on Call 1‑800‑MY‑APPLE

or

See a list of Apple support and service phone numbers around the world:

Contact Apple for support and service - Apple Support

If you sent a Gift Card from Apple as a gift to your sister:

If the recipient can't find the email with the redeem button, you can resend the gift.

There's a How to: "Resend a gift" section in the following article:

Gift apps, media, and more from Apple - Apple Support

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If you did not purchase the gift card from Apple itself:

There's an article warning: About Gift Card Scams - Official Apple Support

Eg: says:

"If you believe you're the victim of a scam involving Apple Gift Cards, App Store & iTunes Gift Cards, or Apple Store Gift Cards, you can call Apple at 800-275-2273 (U.S.) and say "gift cards" when prompted".

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Trouble-shooting: If you have the serial number and receipt

See what to do: If you can't redeem your Apple Gift Card or App Store & iTunes Gift Card - Apple Support

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It seems from the question you posted, you are still using iOS 11 on your iPhone 7 plus

The more up-to-date a device is. generally the more secure it is. (iPhone 7 plus can update to iOS 15.8.2)

If you wish: you can check for updates in Settings > General > Software updates.

(NB: it is always wise to back-up your data before updating).

All the best :-)