ACS: Query Places Based on Array of Place IDs

I am trying to query ACS Places based on an array of place IDs. My code looks like this:

Cloud.Places.query({
    per_page: 30,
    where: {
        place_id: {
            '$in': ["506dc85a025afe7c2207100b","507f29659fdb0155d00003c9"]
        }
    }
}, function (e) {
    if (e.success) {
        callback(e);
    } else {
        alert('Error: ' + ((e.error && e.message) || JSON.stringify(e)));
    }
});

This search returns 0 results (and I have Places with these IDs). I also tried using "id" instead of "place_id" for the "where" parameter. Do you have an idea what I'm doing wrong? Should I be using "search" instead of "query"?