Apple checkout problem
I'm trying to buy a 15 inch MacBook Air (M5, 512GB storage, 24GB RAM, Sky Blue) on Apple's education store, paying with a combination of 5 Apple Gift Cards (bought from the GCX app) plus my credit card. However, each time I hit the "continue with payment" button, I'm met with the same error: "Your payment authorization failed. Please verify your information and try again, or try another payment method."
I've tested this with three different payment methods — my debit card, Apple Pay, and my dad's credit card — and all three failed in the same way. I also spent 30 minutes on the phone with Apple Support, was transferred 4 times, and spoke with 3 specialists. They sent me an email titled "Apple Store Quotation," which contained a link that supposedly would fix my problem, but also resulted in the same error message.
By this point, I'm completely stuck, and frankly not sure what to do. It's not an issue with my cards, since I was able to buy packages from Amazon a few days ago. I also suspected that it was because I was using a VPN, so this was some kind of security precaution, but the purchase didn't go through even after I turned off my VPN. So if someone here encountered this before or knows something I don't, I would really appreciate it!