Cai Yun coupons can be used in the subway. According to relevant information, people who have shopped in Metro Supermarket for many times know that Metro has electronic shopping vouchers, which are issued by Metro and can be used to deduct cash when checking out. It is common in metro stores all over the country. It is very convenient to show the QR code of the shopping voucher to the clerk for verification when checking out, and the shopping voucher also has different face values.