These are "open-loop" prepaid cards that function just like standard debit or credit cards.
The ability to buy an iTunes (Apple) gift card with another gift card depends entirely on the type of gift card you are holding and where you shop. 💳 Option 1: Using a Visa, Mastercard, or Amex Gift Card can you buy an itunes card with a gift card
Most major retailers explicitly ban using their store gift cards to buy third-party gift cards (like Apple or gaming cards) to prevent fraud and money laundering. These are "open-loop" prepaid cards that function just