The main card and the auxiliary card of a credit card are two cards using the same account. No matter the secondary card of the main card, the repayment transaction points to the same credit account, so there is no substantive difference. The consumption of the secondary card can be repaid directly with the main card. The secondary card can repay the debt of its own card, but it cannot repay the debt of the primary card. The main card can also pay the arrears of the subsidiary cards. Many banks print the sub-card bill and the main card bill on a piece of paper, or print them separately, but send them to the payment address of the main card holder.

If you have other specific questions, I suggest you call the customer service staff of the bank, hoping to help you.