@Cali_Claudster Could it be that you’re BigQuery? Custom Column is currently not available:
https://github.com/metabase/metabase/issues/9382 - upvote by clicking on the first post
Doing this should work:
SELECT `source`.`MyBinning`, count(*) AS `count`
FROM (SELECT CASE WHEN `sidedoor_net` < 100 THEN '0-99' WHEN `sidedoor_net` < 400 THEN '100-399' ELSE '400 or greater' END AS `MyBinning` FROM `analytics_prod.settlements`) `source`
GROUP BY `source`.`MyBinning`
ORDER BY `source`.`MyBinning` ASC