The supplementary card is a supplementary card to the main card, and consumption is recorded into the main card account. The way to use this kind of card is that the parent holds the main card and the child holds the secondary card. The child's consumption is included in the parent's account. If SMS notifications are enabled, the parent can also monitor the child's consumption. This kind of card is mainly convenient for the secondary card holder to use, and the main card holder can repay the card.