code: def add(self, quote_id, coupon_code, store_view=None):
          
          return bool(
              self.call('cart_coupon.add', [quote_id, coupon_code, store_view])
          )
docs: Add a coupon code to a quote.
  
          :param quote_id: Shopping cart ID (quote ID)
          :param coupon_code, string, Coupon code
          :param store_view: Store view ID or code
          :return: boolean, True if the coupon code is added