Get to know get_payment_methods
get_payment_methods returns a list of stored payment methods. Use this function to find the ('billing_info_id') ID of your desired payment method for use with billing.pay_invoice.
get_payment_methods expects no parameters.
Array ( [status] => 1 [data] => Array (  => Array ( [billing_info_id] => 5930 [payment_type] => cc [clientid] => 5974 [fname] => Firstname [lname] => Lastname [company] => [address] => 6930 E Chauncey Ln [city] => Scottsdale [state] => [zip] => 85045 [country] => [phone] => [email] => [last_txn_id] => [cc_expire] => 0713 [cc_num] => 4444 [cc_type] => mastercard ) ) )