How to get client name from current time entry

I would like to get the client name (or eventually client id) from the current time entry. In the docs (Time entries | Toggl Engineering) there is the client_name field in the response, whose description is “Related entities meta fields - if requested” but I can’t request it. I tried to use the query parameter meta=true or with_related_data=true but I don’t get the client name of the current time entry in the response.
How can I do it?