I'm trying to exclude records from a query by using a "NOT IN" clause, but it's not giving me what I want. I even tried "NOT LIKE"

I need to exclude the string 'Dev or internal testing' from a column with a mixture of blank cells, but when I run the query it seems to exclude the blank cells as well... and it shouldn't, it should only exclude the cells with the string 'Dev or internal testing'

Here's a copy of my query:

SELECT *
FROM  "Table1"
 WHERE  "activated"  between '2023-04-01'  and  '2023-04-30'
 AND "Reason" NOT IN ('Dev or internal testing')