I think the best way for you to resolve this issue is to use the full query being used when you enter that filter. Open up the folio app in SkySpark you are connecting too and first run the query for the rule you are interested in.
Example for querying a rule from the demo database with no filter:
Assuming this is succeeds, now attempt to put in your filter into the last .findAll() section just before the .sparkHis() section:
If this request succeeds, then copy paste the filter portion directly out of SkySpark and paste it into the filter portion of Niagara. If it still fails, then there is a syntax issue with the filter component you have provided and will need to refer to SkySpark/axon documentation to resolve those types of syntax issues.