The secondary card is a credit card that is applied or reapplied at the same time as the primary card, and the overdraft limit is the same as that of the primary card, that is, the total overdraft limit of the two cards cannot exceed the limit applied by the primary card. However, the main card can limit the consumption amount of the auxiliary card, and the auxiliary card of the main card also has its own expenses, which are calculated separately, but any card can repay the bill when it is sent to the main card.