The GCs that many people on this thread are buying through the shopping portal are digital prepaid visa debit cards through giftcards.com, particularly when they offer 3x miles. The GCM egift ones that they sell can be added to digital wallets and therefore can be used in stores which accept tap-to-pay. They are especially nice because they earn a 1% giftcards.com store credit, thus effectively reducing the fee on a $250 card from $5.95 to $3.45.

Are you buying physical prepaid debit cards from giftcards.com? Or some other site that offers miles through the shopping portal?