If you are accessing the REST API, I recommend using the documentation at https://api.airtable.com. It is much more complete. To filter the results from the REST API, the value for filterByFormula needs to be a valid Airtable formula (url encoded). This works best if you build the formula first in an Airtable formula field. The query you include in your example does not look like a valid Airtable formula.
Also, the results that you show in your post do not look like the results of the public REST API for Airtable.