Hi @trishmalloy , thank you for your post.
You should need the below expression:
concat('19-', <ID of item>)
so, it should be more like:
concat('19-', item('When_an_item_is_created'))
But please double check the syntax of "ID of item"
If you have found my post helpful, please mark thumbs up.
Any other questions, just ask.
Thanks, Alan