AJAX JQuery POST Bad Request

I am trying to submit a form that contains both text and files and I am trying to use POST method in AJax but first it kept saying that Post method is not supported then now it shows me this

jquery.min.js:4 POST http://localhost:8000/register/ 400 (Bad Request)

(I am using django and python for the backend )

Here is my code

$("form#formdata").submit(function(){

var formData = new FormData($(this)[0]);

$.ajax({
    url:  "http://localhost:8000/register/",
    type: 'POST',
    data: formData,

    done: function (data) {
        alert("Done")
    },
    cache: false,
    contentType: false,
    processData: false,

});

return false; });