Re: "Why didn't I receive my Apple Gift Card?"
We are all Apple users, like yourself, in the Community.
We have no access to your accounts or details to in order to find out for you.
If the purchase was made through Apple:
You can check the emailed receipt from Apple for any details on using the gift card.
You might want to check your purchase history to see if the purchase is listed:
View your purchase history for the App Store and other Apple media services - Apple Support
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Re: Perhaps because icloud was full or the email was incorrectly specified.
You might want to check the email didn't go to your "bulk" "spam" or "junk" email folder
If needed: You can use this link to contact Apple: Apple Support
NB: Be aware of scams involving Apple gift cards.
About Gift Card Scams - Apple Support