If plastic bag, swiping up, don't work but vending machine does, try facing the magnetic strip the wrong direction. I've had this issue on a SM vgc and the 150yo yellow vest took my card out of my hand, said I had to swipe it backwards on these machines, swiped it, looked at It, and then got that angry Anti Money Laundering Task Force face that they get. So I said thanks and left with my card. Don't let people touch your cards.