I got the Skymiles Gold card yesterday and was able to use the instant card number to make two flight reservations on Delta. However, I couldn't use the same card details to make a Delta Stay reservation today or add it to my Apple Pay. I called Amex and they say the instant card number can only be used for airline reservations, and there's nothing I can do to use it elsewhere before I get the physical card. Is this response accurate? Should I HUCA?