Those plugins should not matter, I disabled them anyway.
After turning on debug mode, this is the error showing:
1054 Unknown column 'h1.coupon_id_entered' in 'where clause'
/usr/www/users/allisx/libraries/joomla/database/driver/mysqli.php:665
Even though you are using the latest version 3.5.7.0, your database looks like it is out of sync. Please run these sql queries
ALTER TABLE #__awocoupon_history MODIFY coupon_id INT;
ALTER TABLE #__awocoupon_history ADD COLUMN `coupon_code` varchar(255) AFTER coupon_id;
ALTER TABLE #__awocoupon_history CHANGE coupon_entered_id coupon_id_entered INT;
ALTER TABLE #__awocoupon_history ADD COLUMN `coupon_code_entered` varchar(255) AFTER coupon_id_entered;
UPDATE #__awocoupon_history h, #__awocoupon c SET h.coupon_code=c.coupon_code WHERE c.id=h.coupon_id;
UPDATE #__awocoupon_history h, #__awocoupon c SET h.coupon_code_entered=c.coupon_code WHERE c.id=h.coupon_id_entered;
Where #__ is your database prefix. This should fix the issue.
