They had no back up, so reverted to cash only. Cash is a back up, and probably one of the most robust back ups possible in the event of a technology failure. I

They had no back up, so reverted to cash only. Cash is a back up, and probably one of the most robust back ups possible in the event of a technology failure. It is, however, unfortunate that many customers have given up having more than one form of payment. Paying tomorrow is also a form of back up. Which back ups are chosen is a trade off and introduce their own risks (in this case, risk that the form of payment is one that people increasingly don't have, or the risk that you won't be back tomorrow to settle up).