WordPress databasefout: [You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near ')
AND meta_key IN ('attribute_doelgroep','attribute_aantal-personen-voor-s...' at line 3]
SELECT post_id as variation_id, meta_key as attribute_key, meta_value as attribute_value
FROM wp_postmeta
WHERE post_id IN ()
AND meta_key IN ('attribute_doelgroep','attribute_aantal-personen-voor-sessie')
