POSTING an array of objects to node.js/save to database using mongoose

I have a ReactJS form, in which you can dynamically add form "parts"(sections with form input). Here's an example of what I mean by "parts":

<div>
    <input placeholder="Author" />
    <input placeholder="Age" />
    <input placeholder="Amount of books written" />
</div>

Something like this. You can add as many of these divs as you like.

I'm saving the values of these inputs in the state, which gives me a nested array like so:

this.state = {
    formdata : [
        {author: "somebody", age: 34, books: 0},
        {author: "somebody else", age: 100, books: 1}
    ]
 }

Right now I'm use axios post to post the data to node.js with express. This is my post function:

handleSubmit(e) {

    axios.post('receivedata',
        querystring.stringify({
             formdata : this.state.formdata
        }), {
            headers : {"Content-Type": "application/x-www-form-urlencoded"}
            }
        )
        .then(function (response) {
            console.log(response);
        })
        .catch(function (error) {
            console.log(error);
        });
}

And this is the mongoose schema that I use:

var EntrySchema = new mongoose.Schema({
    formdata: [{type:String}],
    updated_at: {type: Date, default: Date.now}
});

and this is how I (try to) send the data to my database:

router.post("/", function(req, res) {

    newEntry.formdata = req.body.formdata;
        newEntry.save(function (err) {
            if(err)
                res.send(err);
            res.send("Entry added successfully!");
        });
    });

That doesn't work though and when I check the database, I receive an array with an empty string like so: formdata:[{""}]

I think the problem is with how the schema is set up, since, when I do console.log(this.state.formdata) it correctly returns the data. My next guess would be that axios is not able to send nested array, but after some research I found that that's not the case so I'm assuming that there's a special way to define nested arrays in the mongoose schema? How would I go about that?

Edit: I was thinking that maybe I could do something along the lines of:

var EntrySchema = new mongoose.Schema({
    formdata: [{
        author: String,
        age: Number,
        books: Number
    }],
    updated_at: {type: Date, default: Date.now}
});

I tried this and it doesn't work either. Now, I don't know if I'm on the right track or how else to do this. I also tried changing the Content-Type in the header to "application/ json", as suggested in another answer. Once again, it didn't work.

Any help is appreciated.