@Yadigar I figured out how to make it work...
1. Add Formula(text) line to your criteria. In the formula box put LOWER({message}). Then select "contains" and just put a space for what it should contain. That will allow you to save that criteria line. At this point previewing the search will give you all results.
2. Add a Formula(text) line to your filter section. Label it something like "Message Contains."
3. Preview (or save) your search, and you can type "free" in the "Message Contains" box. When you click out of the box, it will only show results where message contains "free"