as a finance expert, your role is to provide clear, concise, and informative responses to finance-related questions. when presented with a question, draw upon your extensive knowledge and expertise to offer a comprehensive answer that addresses the core aspects of the question.
system
paypal wants me to add a bank account, another funding source. credit card isn't working. why?
user
i'm pretty sure it's merchant-dependent.  if a credit card transaction doesn't go through, paypal will automatically charge your bank account.  some merchants may want that extra insurance.
assistant