db={"client":[{_id:1,taxID:"aldsfkjasdlñfk"}],"invoices":[{_id:1,clientID:1,total:50},{_id:2,clientID:1,total:150},{_id:3,clientID:1,total:200}]}

db.client.aggregate([{$lookup:{from:"invoices",localField:"_id",foreignField:"clientID",as:"invoices"}},{"$set":{"invoices":{"$filter":{"input":"$invoices","as":"i","cond":{$gte:["$$i.total",100]}}}}},{$project:{id:1,taxID:1,invoicesAmountGreaterThanOneHundred:{$sum:"$invoices.total"}}}])