Getting a blank report after adding a parameter to main query. The parameter is for selecting a URL from a drop down. The main query works fine using a hardcoded URL.

In the main query (LastResultQuery) I'm attempting to match on base_url = to the parameter

If I attempt to get fields, I get an error "Unexpected error retrieving fields from Mongo..."

When I remove the parameter from my main query (LastResultQuery) and hardcode the URL the report works as expected and returns only the data for the selected URL.

Here is the query for the parameter: and the fields:
Previewing the query for the parameter returns the two URLs I would expect and the parameter shows up correctly on the report.

Here is how the parameter is setup:

I feel like it's a syntax issue but cannot seem to figure out where I've gone wrong. Any guidance on how to trouble-shoot this would be appreciated.

Thanks in advance!