CITI (AA Advantage card) is a no-go for me to buy SMGC's.
Every time I try to buy one or more of them, CITI declines the purchase and I have to confirm with them that the purchase is legitimate. However, when Simon gets a decline on a credit card, you cannot use that card again for 24 hours, making it impossible to use for GC purchases that day.
No matter how hard I have tried to preempt Citi in order to prevent their declining the purchase, I have never succeeded no matter how small the GC amount.
So I have no idea if you can use CITI cards for MS. I can't.