What debugging techniques can be used in PHP to troubleshoot issues with Ajax requests and dropdown selection synchronization?

Issue: When troubleshooting issues with Ajax requests and dropdown selection synchronization in PHP, one common technique is to use the `console.log()` function in JavaScript to log the data being sent and received in the Ajax request. This can help identify any errors or inconsistencies in the data being passed between the client-side and server-side code. Another useful technique is to use the `var_dump()` function in PHP to print out the contents of the data received from the Ajax request. This can help verify that the data is being correctly received and processed by the server-side code. Additionally, checking the network tab in the browser's developer tools can provide valuable information about the Ajax request, including the request and response headers, status codes, and any error messages that may be occurring.

<?php
// Check if the request is an Ajax request
if(isset($_SERVER['HTTP_X_REQUESTED_WITH']) && strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) == 'xmlhttprequest') {
    
    // Get the data sent in the Ajax request
    $data = $_POST['data'];
    
    // Process the data as needed
    // For example, synchronize dropdown selections based on the received data
    
    // Send a response back to the client
    echo json_encode(['success' => true]);
    
} else {
    // Handle non-Ajax requests here
    echo 'Invalid request';
}
?>