The secondary card must be consistent with the main card and share the credit line with the main card. Without an independent account, you can't log in to online banking or make bills independently. Repayment is included in the main card account, so it is ok.

The main cardholder is in a dominant position and has the right to decide to add or cancel the secondary card. If the primary card is cancelled, the secondary card should be returned to the card issuer voluntarily. When the cardholder of the primary card requests to stop using the secondary card, he should also return the secondary card to the card issuer, and the outstanding debt will still be borne by the cardholder of the primary card.