SQL how sum if value

Hi I try to need to sum values and if there is more than 20 there shouldbe written 20 else should be number.

I don't know what i make wrong:

SELECT
    ta6.product_product_id AS ID,
    ta6.product_manufacture_code AS Code,
    SUM(CASE WHEN ta3.stock_quantity >= 20 THEN 20 ELSE ta3.stock_quantity END) AS Quantity,
    ta4.price_value AS Price,
    ta5.Attribute_Value AS Sizer,
    ta6.Procut_product_name AS Name,
    ta7.Attribute_Value AS produce
FROM
    product ta6
LEFT JOIN stock ta3 ON
    ta3.stock_id = ta6.product_id
LEFT JOIN price ta4 ON
    ta4.price_id = ta6.product_id
    AND ta4.price_type = 2
LEFT JOIN Attributes ta5 ON
    ta5.Attributes_product_Id = ta6.product_id
LEFT JOIN Attributes ta7 ON
    ta7.Attributes_product_Id = ta6.product_id
WHERE
    ( ta3.stock_wharehouse_id = 1
    AND ta5.Attrib_id = 54
    AND ta7.Attrib_id = 25 )
GROUP BY
    ta6.product_manufacture_code,
    ta6.product_product_id
    ta4.price_value,
    ta5.Attribute_Value,
    ta6.product_product_name ,
    ta7.Attribute_Value;

Table stock_quantity looks like: Stock_table image

How to sum it ??