As soon as you create a master card (for example; for Customer), the system will automatically create a financial account for the type -> "Customer".
If you do not want to create separate master cards, you can add another financial account to the customer card as financial account type -> "Supplier".
Thus, by adding two financial accounts to the same master card, it is reflected that the person/company is both a supplier and a customer.
Appropriate Financial Account Types for Customer Current Accounts
As explained above, on master cards registered in "ACS - Customer", you can create multiple financial accounts with the following financial account types: