Вы не можете использовать агрегатную функцию над другой.Вам нужно разделить запросы:
SELECT SUM(amount) As Amount
FROM
(
SELECT tcc.entry_fees*COUNT(tccc.match_contest_id) as amount
FROM `tbl_cricket_customer_contests` tccc
LEFT JOIN tbl_cricket_contest_matches tccm on(tccm.id=tccc.match_contest_id)
LEFT JOIN tbl_cricket_contests tcc ON (tcc.id=tccm.contest_id)
WHERE tccc.customer_id = 9 GROUP BY tccc.match_contest_id
) As DT
Обновление
Как я уже писал в комментариях, я не эксперт MySql, но я думаю, что это то, чтовы ищете.
Примечание. Я закомментировал предложение group by
во внешнем запросе.
SELECT tc.*,
(
SELECT SUM(amount) As Amount
FROM
(
SELECT tcc.entry_fees*COUNT(tccc.match_contest_id) as amount
FROM `tbl_cricket_customer_contests` AS tccc
LEFT JOIN tbl_cricket_contest_matches AS tccm on(tccm.id=tccc.match_contest_id)
LEFT JOIN tbl_cricket_contests AS tcc ON (tcc.id=tccm.contest_id)
WHERE tccc.customer_id = tc.id GROUP BY tccc.match_contest_id
) As DT
) as spendamount
FROM `tbl_customers` As tc
WHERE tc.`is_deleted` = 'N'
-- Do you really need that group by here? GROUP BY tc.`id`
ORDER BY tc.`spendamount` DESC