Mongodb $lookup how to join a field with $id to $id.toString

Question

I have a two collections

Collection1

{
    _id: ObjectId("5ba27d02d579d8cd47a02408"),
    NAME: "xxxx",
    DESC: "xxxxxx"
}

Collection2

{
    _id: ObjectId("5ba2900dd579d8cd47a026b7")
    COLLECTION1_ID: "5ba27d02d579d8cd47a02408"
    ORDER: 5
}

I'm trying to join both the collections using the following code but it doesnt seem to work, is there something I am missing? I'm doing this on Spring boot and maven version 3.7.0

MongoDatabase database = mongo.getDatabase("ngdesk");
MongoCollection<Document> collection = 
database.getCollection("Collection1");

ArrayList<Bson> filters = new ArrayList<Bson>();

filters.add(Aggregates.lookup("Collection2", "_id", "COLLECTION1_ID", "TEST"));

List<Document> testList = collection.aggregate(filters).into(new ArrayList<Document>());