The IBAN is the only distinguishing item on the back side of the card that indicates if you are creating a Maestro card for the right account.
As a new Bunq user (UX designer) I was searching like crazy how to create a Maestro card for a second (sub)account... after searching, cursing and creating a lot of unnecessary cards, I finally found out that the IBAN indication is actually a SELECT BOX!
Please give new user a slight hint of that item actually being of great importance in selecting the right account for the card. Also please indicate the name of the subaccount somewhere too, because you easily get lost in numbers with the amazing functionality of having multiple sub accounts.
Thanks on behalf of all new users!