code: func (r Product_Order) RequiredItems(itemPrices []datatypes.Product_Item_Price) (resp []datatypes.Product_Item, err error) {
  	params := []interface{}{
  		itemPrices,
  	}
  	err = r.Session.DoRequest("SoftLayer_Product_Order", "requiredItems", params, &r.Options, &resp)
  	return
  }
docs: // Get list of items that are required with the item prices provided