Achievement Summary REST API returns "id' must be a valid Guid."

I'm making what I think is a simple call to get the the achievement summary information as outlined in List Summaries Achievement REST Endpoint - API Documentation - Verint Community 11.x - Verint | Telligent Community.

But I'm getting back an error stating: 'Id' must be a valid Guid.

According to the above linked documentation, none of the possible parameters are mandatory, so I'm a little lost as to the GUID it wants.