$(document).ready(function(){
 $('.trolley').click(function(){
  $(this).find('i').toggleClass('open'); // call the icon class in h3 class and add .open
  $('.addbar').toggleClass('open');
 });
 
 $('.a1').click(function(){
  var qunti = $('#itemnum1').val();
  var id = $('#hidden1').val();
   $.ajax({
    url:"Promotionaddajax.php",
    method:"post",
    async: false,
    data:{
     "cart": quanti,
     "item": id
    },
    success:function(data)
    {
     $('#itemnum1').val('');
    }
   });
 });
});

these are my ajax code I was trying to insert a row of data into database after click on .a1 my code are correct, but it's not working here is my Promotionaddajax.php code.

<?php
session_start()
include "include/conn.php";

 $sql = "SELECT * FROM users WHERE User_ID = (SELECT User_ID  FROM users WHERE Username = '".$_SESSION['username']."')";
  
 $result = mysqli_query($conn, $sql);
  
 $row = mysqli_fetch_array($result);
 $userid = $row['User_ID'];
 $quanti = $_POST['cart'];
 $itemid = $_POST['item'];
 
 $addcart = "INSERT INTO cart (cart_quantity, coupon_id, User_ID) VALUES ('$quanti', '$itemid', '$userid')";
 mysqli_query($conn, $addcart);
?>