Remove multiple documents from mongo in a single query

You need to pass the ids in a specific format using ObjectId():

db.users.remove({_id: {$in: [ObjectId('Item1'), ObjectId('Item2'), ObjectId('Item2')]}});

Remove doesn't accept integer - you have to use ObjectId instance with _id format as a string.

db.users.deleteMany({'_id':{'$in':inactive_users}})

List them all and use $in operator:

db.users.remove({_id:{$in:[id1, id2, id3, ... ]}})

var collection = db.users;
var usersDelete = [];
var ObjectID = req.mongo.ObjectID;   //req is request from express

req.body.forEach(function(item){     //req.body => [{'_id' : ".." , "name" : "john"}]
    usersDelete.push(new ObjectID(item._id));
});

collection.remove({'_id':{'$in': usersDelete}},function(){
    //res.json(contatos);
});