I recently was at a sporting event and decided I was hungry and wanted to buy something to eat.  I spotted a vending machine tucked in the corner of a stairwell that sold small snacks and drinks.  I approached the vending machine and looked through the glass to decide what I wanted.  I found a bag of chips that I know I like and decided that is what I would buy.  I read the price of the chips was one dollar.  I reached into my wallet and retrieved the dollar needed to purchase the chips.  I looked back into the vending machine and found that the chips were located in the B4 position.  I put my dollar into the machine and pressed the "B" button and then the "4" button.  The coiled metal rotated and the bag of chips fell to the bottom of the machine.  I reached through the door at the bottom and retrieved my chips.
How did they pay?