code: def create(self, store_id, order_id, data):
          
          self.store_id = store_id
          self.order_id = order_id
          if 'id' not in data:
              raise KeyError('The order line must have an id')
          if 'product_id' not in data:
              raise KeyError('The order line must have a product_id')
          if 'product_variant_id' not in data:
              raise KeyError('The order line must have a product_variant_id')
          if 'quantity' not in data:
              raise KeyError('The order line must have a quantity')
          if 'price' not in data:
              raise KeyError('The order line must have a price')
          response = self._mc_client._post(url=self._build_path(store_id, 'orders', order_id, 'lines'))
          if response is not None:
              self.line_id = response['id']
          else:
              self.line_id = None
          return response
docs: Add a new line item to an existing order.
  
          :param store_id: The store id.
          :type store_id: :py:class:`str`
          :param order_id: The id for the order in a store.
          :type order_id: :py:class:`str`
          :param data: The request body parameters
          :type data: :py:class:`dict`
          data = {
              "id": string*,
              "product_id": string*,
              "product_variant_id": string*,
              "quantity": integer*,
              "price": number*
          }