Insert embedded document in mongodb via angularjs

I am trying to insert embedded document in MongoDB through AngularJS. Parent document is existing. This is schema of embedded document

offers: [{
        date: Date,
        offer: {
            id: mongoose.Schema.ObjectId,
            added: {
                type: Date,
                default: Date.now()
            },
            displayName: String,
            creator: Number,
            //creator: {
            //    type: mongoose.Schema.Types.ObjectId,
            //    ref: 'User'
            //},
            photo: String,
            description: String,
            additional: {
                name: String,
                data: String
            }
        },
        linkedBy: Number
    }],

This is my router

router.post('/',expositionController.create);
router.get('/',expositionController.getAll);
router.get('/:id',expositionController.get);
router.put('/:id',expositionController.update);
router.delete('/:id',expositionController.delete);

router.post('/:id/offer',expositionController.createOffer);

Create offer method in controller

exports.createOffer = function(req,res){
    var id = req.params.id;
    try{
        id = new ObjectId(id);
        Exposition.findById(id,function(err,exposition){
            if(err){
                res.send(err);
            }
            exposition.offer = new Offer(req.body.offer);
            exposition.save(function(err){
                if(err)
                    res.send(err);
                res.json({message: "Ok"});
            });
        });
    }catch(e){
        res.send(404);
    }
};

Here is code from AngularJS controller with inserting of offer

$scope.createOffer = function (_id) {
            var offerResource = new OfferResource();
            offerResource.offer = new OfferUpdateService();
            offerResource.offer.name = $scope.offer.name;
            offerResource.offer.photo = $scope.uploadPhoto;
            offerResource.offer.description = $scope.offer.description;
            offerResource.$save(function (result) {
                $scope.offer.name = '';
                $location.path("/exposition/")
            });
        };

And AngularJS routing

$stateProvider
.state('offer', {
                url: "/:id/offer/",
                templateUrl: 'app/exposition/listOffers.tpl.html',
                controller: 'ExpositionsController'
            })

When I am trying to insert an offer, I got an error

http://localhost:3000/exposition/offer 404 not found

Whan am I doing wrong?

Thanks!