WP_safe_redirect not working

Your action callback probably gets called, but it could be that the if-statement that just fails. Are you using the default “category” taxonomy (i.e. Dashboard > Posts > Categories) or a custom taxonomy (i.e. Dashboard > {my-post-type} > {my-taxonomy}) as the project category?

If you’re using a custom taxonomy, then you should use is_tax(‘my-taxonomy’) instead of is_category() as the latter checks for the default category, not custom ones.

But, you can temporarily add a die('it works'); to your callback also, before the if statement, to verify that it gets called.