I have a hook to do a few things when a custom post is published. The hook takes my new post and turns it into a child category in custom taxonomy 'product_category'. That part works:
BUT _app_cat_id value is not being updated. It's just being added to the db with no value. When I var_dump $post_ID and $new_term_id (before the update post meta line) they both have the correct values, and I added 'blue' just to see if it was a variable issue but the db meta value is still blank. What's preventing it from working?