order by not working on alias column in mysql query with union all query

SELECT SUM(T1.approve_con) AS compl_rec,
SUM(T1.payout) AS payout,
SUM(T1.reversal) AS reversal,
T1.app_id,
T1.end_user,
T1.created
FROM (
    (SELECT app_id,end_user,created,
    approve_conversions AS `approve_con`,
    '0' AS reversal,
    payout AS payout
    FROM app_end_users 
    WHERE publisher_id=1625 
    AND app_id=57)
UNION ALL
    (SELECT opinongold_survey_response.app_id,
    opinongold_survey_response.user_id AS end_user,
    opinongold_survey_response.movement AS created,
    (CASE WHEN opinongold_survey_response.survey_status= 'Completed' THEN 1 ELSE 0 END) AS `approve_con`,
    (CASE WHEN opinongold_survey_response.survey_status= 'Rejected' THEN 1 ELSE 0 END) AS reversal,
    (CASE WHEN opinongold_survey_response.survey_status= 'Completed' THEN payout ELSE 0 END) AS payout                                  
    FROM opinongold_survey_response
    WHERE  pub_id=1625 
    AND app_id=57)
) AS T1
GROUP BY T1.app_id,T1.end_user
ORDER BY `approve_con` DESC
LIMIT 0, 10   

above is my mysql query order by is not working on approve_con, payout, reversal column please let me where i am doing wrong in this query.