def customer_outstanding_invoices(code = nil)
      now = Time.now
      customer_invoices(code).reject do |i| 
        i[:paidTransactionId] || i[:billingDatetime] > now
      end
    end
def customer_outstanding_invoices(code = nil)
      now = Time.now
      customer_invoices(code).reject do |i| 
        i[:paidTransactionId] || i[:billingDatetime] > now
      end
    end
Returns an array of any currently outstanding invoices for the given customer.

code must be provided if this response contains more than one customer.