Post Update with PDO does not update in database

Maybe this is a duplicate question, but for all answers i found here and elswhere, i can't get it to work. I'm trying to update a few short php files which use mysqli to PDO to be future proof. I'm sending a value to the PHP file from out of Livecode, now this al worked with PHP and MySQL. But with PDO....not yet, i'm testing localhost the connection works:

<?php
//PDO
$servername = "localhost";
$username = "root";
$password = "";

try {
$pdo = new PDO("mysql:host=$servername;dbname=mydatabase", $username, $password);
// set the PDO error mode to exception
$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
echo "Connected successfully"  . "<br />"; 
}
catch(PDOException $e)
{
echo "Connection failed: " . $e->getMessage();
}
?> 

Then this part is not working, it's not updating

<?php
//1. Create a database connection
$config = include_once "connect_database.php"; 
//2. Perform database query
$sql = "UPDATE `flash` SET `flashnews`= :flashnews WHERE `id`= :id";
$stmt = $pdo->prepare($sql);                                  
$stmt->bindParam(':flashnews', $_POST["flashnews"], PDO::PARAM_STR);       
$stmt->bindParam(':id', $_POST["id"], PDO::PARAM_INT);   
$stmt->execute();  
?>

Anyone has a clue what is wrong? thanks for any help on this.