the question and description says the following
"Great! That query doesn't take refunds into account. We'll update the query to exclude refunds.
Fields like refunded_at will only have data if the transaction was refunded, and otherwise left null."
"Update our daily revenue query to exclude refunds. Complete the query by filtering for refunded_at is not null."
wouldn't this include the refunds, NOT exclude them? since you and leaving the ones without a null value to be calculated?