Both the supplementary card and the main card use one fund account. The supplementary card can be said to be a derivative of the main card. The premise for the existence of the supplementary card is the existence of the main card. What is used is the main card. Funds and credit limit, and the amount of overdraft consumption will eventually be returned by the primary card applicant. However, the principal cardholder and the supplementary cardholder are jointly and severally liable to each other for repaying the amounts owed. Therefore, if the main card owes money and the cardholder of the main card is unable to repay it, the cardholder of the supplementary card is responsible for paying off the debt