I see you've already created a hiearchy in the screenshot above.
What sort of field are you trying to drag in? A dimension, correct? What is it's data type? If it is a calculation, what is the calcuation?
Actually, that hierarchy was created by someone else. Is there any way I can add into it? The dimension I'm trying to add in is a text field.
Good morning, Eric,
If you are using a published data source, you need to create a local copy, and change the data source to the local copy. Then you are allowed to add to hierarchies. Hope this is helpful for you.