protected function getWriteableAttributes()
{
return array('account', 'plan_code', 'coupon_code', 'coupon_codes', 'unit_amount_in_cents', 'quantity', 'currency', 'starts_at', 'trial_ends_at', 'total_billing_cycles', 'first_renewal_date', 'timeframe', 'subscription_add_ons', 'net_terms', 'po_number', 'collection_method', 'cost_in_cents', 'remaining_billing_cycles', 'bulk', 'terms_and_conditions', 'customer_notes', 'vat_reverse_charge_notes', 'bank_account_authorized_at', 'revenue_schedule_type', 'gift_card', 'shipping_address', 'shipping_address_id');
}