On the front of CCB's credit card, there is usually a string of numbers, usually the membership number, appearing on his family's joint credit card. Here, take China Eastern Airlines Dragon Card of CCB as an example (a credit card jointly issued by CCB and China Eastern Airlines). The landlord looks at the picture.

Which merchant's member is represented by a string of numbers of the landlord, depending on the actual card type. If it's convenient, you can send a screenshot when you ask, so as to further answer for you.