Wordpress Ajax无法正常工作？

I am developing plugin in wordpress, i used select tag element, i need the value to be stored in the database on change the option values , but it seems ajax is not working .below is my code ,

this is script code

function ajaxFunction(str,id) {
   var payment_selected = str;
    var id=id;
    var queryString = "&id_took=" + id + "&sel=" + payment_selected;
   
    jQuery.ajax({
        var data = {  'action' : 'my_action',
                        'queryString':queryString
            };
      jQuery.post(ajaxurl, data, function(response) {
            alert('Got this from the server: ' + response);
        });
    });

 
    } 

<select  name='payment_select' id="payment_select" onchange="ajaxFunction(this.value,<?php echo $row->id ?>)">   
                            <option value="Payment Due">Payment Due</option>
                        <option value="Payment completed">Payment Completed</option>
                        </select>                       
                        
    /*below one  i have written in my plugin code  */
    <?php
 
add_action( 'wp_ajax_my_action', 'my_action' );

function my_action() {
    
     global $wpdb;
     $id_selected = $_POST['id_took'];
     $id = $_POST['id'];
     $table_name_payment = $wpdb->prefix . "online_booking_system_model";
    if($whatever2=="Payment completed")
{
        
$result_pay = $wpdb->query("UPDATE $table_name_payment SET 
    payment_status = $id_selected
    WHERE id = $id ");
      echo "success";
        
    }
   
}
?>

</div>

Your use of jQuery.ajax seems wrong. Try without wrapping the code with jQuery.ajax like this:

Javascript

function ajaxFunction(str,id) {   
    var data = {  
        'action' : 'my_action',
        'id_took': id,
        'sel'    : str
    };
    jQuery.post(ajaxurl, data, function(response) {
        alert('Got this from the server: ' + response);
    });
} 

HTML

<select  name='payment_select' id="payment_select" onchange="ajaxFunction(this.value,<?php echo $row->id ?>)">   
    <option value="Payment Due">Payment Due</option>
    <option value="Payment completed">Payment Completed</option>
</select>                       

PHP

<?php

    add_action( 'wp_ajax_my_action', 'my_action' );

    function my_action() {

        global $wpdb;
        $id = $_POST['id_took'];
        $str = $_POST['sel'];
        $table_name_payment = $wpdb->prefix . "online_booking_system_model";
        if($whatever2=="Payment completed")
        {            
            $result_pay = $wpdb->query("UPDATE $table_name_payment SET 
            payment_status = $sel
            WHERE id = $id ");
            echo "success";            
        }       
    }
?>