Conga's External Data feature is currently set up to retrieve a list of object records (Entity Collections) only, as opposed to just a single object record (Individual Entity by ID, Individual Property, and Individual Property Raw Value). Do not use query syntax, such as (1) or (3) to attempt to return 1 or 3 specific records. Instead, use additional filters in the query syntax to filter the returned list of data. For more information, see OData's Basic Tutorial.