"inList" filter in "Search Directory Contacts" not working?

Hi,
I have not been able to get the "inList" filter to work on the Search Directory Contacts API. Other filters, yes, but not this one.

I know there is also a get Mailing List Contacts API, but what I am needing to do is search within a mailing list based on another criteria.
EDIT: This is the error message I recieve, even when using the exact syntax from the documentation:
"errorMessage": "The provided simpleFilter syntax is invalid, please review all components before retrying the request",

Has anyone else been able to get this filter to work?
Thanks!