Q: Can't add a new Credit Card

Hi Apple community.

My bank uses virtual credit cards through www.mbnet.pt as an alternative for those who only have a debit card. Apparently, I've reached a limit, since I can't add a new one. I don't need to make any purchases at the moment, but I do need to setup family sharing, and it doesn't let me do so without adding a new payment method.

Does anyone know of a solution for this? Thanks in advance.