Final task #7 question

I’m trying to write query for final task, question #7:

Using the air_alliances and air_routes collections, find which alliance has the most unique carriers(airlines) operating between the airports JFK and LHR , in either directions.
Names are distinct, i.e. Delta != Delta Air Lines
src_airport and dst_airport contain the originating and terminating airport information.

Could somebody please clarify me what’s the problem here, because I’m not getting the right answer:

db.air_routes.aggregate([{"$match":{"$or":[{"$and":[{“src_airport”:“JFK”},{“dst_airport”:“LHR”}]},{"$and":[{“src_airport”:“LHR”},{“dst_airport”:“JFK”}]}]}},{"$lookup":{“from”:“air_alliances”,“foreignField”:“airlines”,“localField”:“airline.name”,“as”:“alliance”}},
{"$group":{"_id":{“airlineName”:"$airline.name",“allianceName”:{"$arrayElemAt":["$alliance.name",0]}},“count”:{"$sum":1}}},{"group":{"_id":"_id.allianceName",“total”:{"$sum":"$count"}}}]).pretty()

thanks in advance