I have a buyer account with several, valid cards associated with it. According to Balanced's documentation the most recently added card is the default funding source. How do I set another, existing card as the default funding source without asking the user to resubmit their card details to create a new card?
You cannot currently set an alternate funding source, the most recently added card is always the default. To debit or credit a specific funding instrument such as a card or bank account you must pass through the URI of the object as the parameter funding_source or funding_destination respectively:
buyer = balanced.Account.find(uri_of_account)
card = buyer.cards[x]
debit = buyer.debit(amount_in_cents, source_uri=card.uri)
merchant = balanced.Account.find(uri_of_account)
bank_account = merchant.bank_accounts[0]
credit = merchant.credit(amount_in_cents, destination_uri=bank_account.uri)