update quantity of product after checkout - php

Question

I am trying to update the item quantity after the finished transaction. I have quantity on my item and I wanted to lessen the item quantity depending on the item ordered. the transaction works fine but the problem is the update does not execute and it does not update the quantity of the item in my table.
the code:
<?php
include 'includes/session.php';
if(isset($_GET['confirmation'])){
$confirmation = $_GET['confirmation'];
$p_quantity = $_GET['p_quantity'];
$date = date('Y-m-d');
$conn = $pdo->open();
try{
$stmt = $conn->prepare("INSERT INTO sales (user_id, confirmation, status, sales_date) VALUES (:user_id, :confirmation, :status, :sales_date)");
$stmt->execute(['user_id'=>$user['id'], 'confirmation'=>$confirmation, 'status'=>1, 'sales_date'=>$date]);
$salesid = $conn->lastInsertId();
$stmt = $conn->prepare("UPDATE products SET p_quantity=p_quantity-:p_quantity WHERE id=:id");
$stmt->execute(['p_quantity'=>$p_quantity, 'id'=>$id]);
try{
$stmt = $conn->prepare("SELECT * FROM cart LEFT JOIN products ON products.id=cart.product_id WHERE user_id=:user_id");
$stmt->execute(['user_id'=>$user['id']]);
foreach($stmt as $row){
$stmt = $conn->prepare("INSERT INTO details (sales_id, product_id, quantity) VALUES (:sales_id, :product_id, :quantity)");
$stmt->execute(['sales_id'=>$salesid, 'product_id'=>$row['product_id'], 'quantity'=>$row['quantity']]);
}
$stmt = $conn->prepare("DELETE FROM cart WHERE user_id=:user_id");
$stmt->execute(['user_id'=>$user['id']]);
$_SESSION['success'] = 'Transaction successful. Thank you.';
}
catch(PDOException $e){
$_SESSION['error'] = $e->getMessage();
}
}
catch(PDOException $e){
$_SESSION['error'] = $e->getMessage();
}
$pdo->close();
}
header('location: profile.php');
?>