Giving error The HTTP status code "600" is not valid. after submitting ajax

InvalidArgumentException in Response.php line 462:The HTTP status code "600" is not valid.

On form submit I got this error

$("#personal_info_form").submit(function(event) {
var name = $("#Name").val();
var email = $("#Email").val();
var mobile = $("#Mobile").val();

if (name != "" && email != "" && mobile != "") 
{
    event.preventDefault(); //prevent default action
    //get form GET/POST method
    $('#main_container').addClass('hidden');
    $('#sub_container').removeClass('hidden');
    var form_data = new FormData(this); //Creates new FormData object

    $.ajax({
        url: 'new_register_flow',
        type: 'POST',
        data: form_data,
        contentType: false,
        cache: false,
        async:true,
        processData: false
    }).done(function(response) { //

        console.log(response);
        var url = response;

        openinatamojo(url);
    });
}

});

via Chebli Mohamed