有效负载不包含JSON

I am trying to post my formdata via Ajax. But for some reason my payload is shown as a string and not as ajax:

shopName=asfd&street=afs&houseNo=asf&zipcode=&city=&country=&phoneNumber=&fax=&email=&website=

But it shouls appear as JSON. I have got no idea what could be wrong.

The code I have to compose my request is:

$('#shopForm').submit(function(e){
e.preventDefault();
var formData = $('#shopForm').serialize();
submitForm(formData);
});

function submitForm(formData)
{
$.ajax({
    url: '/admin/shop/ajax',
    type: 'POST',
    dataType: 'json',
    contentType: 'application/json; charset=utf-8',
    data: formData,
    success: function(response) {
        console.log('succes');
        console.log(response);
    },
    error: function(response) {
        console.log('error');
        console.log(response);
    }

});
}

Any help is well appreciated.

Thanks.

EDIT 1

When changing data: formData, tot data: JSON.Stringify(formData),

The payload changes to

shopName=asfd&street=afs&houseNo=asf&zipcode=&city=&country=&phoneNumber=&fax=&email=&website= No Properties