This catches me probably every 6 months 🙂 You need to have on the form in some way for the Business Rule to work appropriately. Note, it can be hidden on the form so if you want to perform an action based on the field it doesn't need to show, just be on the form.
Hope this helps. Please accept if this answers your question or like if helps in some way.
Hope this helps. Please accept if answers your question or Like if helps in any way. Thanks, Drew