Ajax JSON PHP Stringify未发布但成功返回

我有一个ajax脚本，它从输入中获取值，然后使用MYSQLI插入到mysql数据库中。

当我单击按钮时，会成功返回唯一的id，但没有任何post值插入到数据库中。此外，当单独测试post值时，它们也不会显示为达到了发布的php脚本。

运行此操作后，数据库中会有唯一的id，但不会存储其他信息。

Q. How come the variables not reaching the PHP, thus preventing me from a successful insertion to the database?

Ajax

$('#postData').click(function() {
        smallVan_getForm_values();
    $.ajax({
     type: "POST",
     dataType: "json",
     url: "//xxxxx",
     data: JSON.stringify({
            book_email:book_email,
            book_clientTitle : book_clientTitle,
            book_firstname : book_firstname,
            book_lastname :book_lastname,
            book_dateofbirth : book_dateofbirth,
            book_primarycontactnumber : book_primarycontactnumber,
            book_secondarycontactnumber : book_secondarycontactnumber,
            departing_first_lineaddress : departing_first_lineaddress,
            departing_second_lineaddress : departing_second_lineaddress,
            departing_postcode : departing_postcode,
            destination_first_lineaddress : destination_first_lineaddress,
            destination_second_lineaddress : destination_second_lineaddress,
            destination_postcode : destination_postcode,
            amount : amount,
            book_consignmentdate : book_consignmentdate,
            book_timeofbooking : book_timeofbooking,
            book_additionalnotes : book_additionalnotes
    }),
     contentType: "application/json; charset=utf-8",
        success: function (result) {
        //  alert(result);
            if (result.status == "success"){
                    uniqueID = result.uniqueID;
                    alert(uniqueID);
            }
       }
    });
});
});
//AJAX END

PHP

if(isset($_SERVER['HTTP_X_REQUESTED_WITH']) && !empty($_SERVER['HTTP_X_REQUESTED_WITH']) && strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) == 'xmlhttprequest')
{ //if request made from localserver then proceed here
    insertData();
}

function insertData() {
$uniqueID = substr(str_shuffle(str_repeat("0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWYXZ", 10)), 0, 10);

    $conn=mysqli_connect("xxxx","xxx","xxxxx^","xxxxx");
    // Check connection
    if (mysqli_connect_errno())
      {
      echo "Failed to connect to MySQL: " . mysqli_connect_error();
      }
    // Perform queries
    mysqli_query($conn,"INSERT INTO bookings_table ( booking_uniqueID , book_email , book_clientTitle , book_firstname , book_lastname , book_dateofbirth , book_primarycontactnumber , book_secondarycontactnumber , departing_first_lineaddress , departing_second_lineaddress , departing_postcode , destination_first_lineaddress , destination_second_lineaddress , destination_postcode , amount , book_consignmentdate , book_timeofbooking , book_additionalnotes )
   VALUES ( '$uniqueID' , '$_POST[book_email]' , '$_POST[book_clientTitle]' , '$_POST[book_firstname]' , '$_POST[book_lastname]' , '$_POST[book_dateofbirth]' , '$_POST[book_primarycontactnumber]' , '$_POST[book_secondarycontactnumber]' , '$_POST[departing_first_lineaddress]' , '$_POST[departing_second_lineaddress]' , '$_POST[departing_postcode]' , '$_POST[destination_first_lineaddress]' , '$_POST[destination_second_lineaddress]' , '$_POST[destination_postcode]' , '$_POST[amount]' , '$_POST[book_consignmentdate]' , '$_POST[book_timeofbooking]' , '$_POST[book_additionalnotes]' )");
    mysqli_close($conn);
    echo json_encode(array('status' => 'success', 'uniqueID' => $uniqueID));
}