Problem w Adding Tags to File Name (and Title)

No, the problem is the action type. If you want to assign new data to a field then use an action of the type "Format value".

The most straight-forward way to rename files would be the converter, in fact. and that is mentioned in the HowTos

and the documentation.

If you insist on an action, the search function in this forum reveals with the search word "rename file" e.g. the following thread: