Google App Engine showing only index.php file

I deployed my PHP application for the first time on Google App Engine via Google Cloud SDK CLI. it contains 4 php files. All the php files are in the same folder.

Here is my issue. When I run my application, it only shows content of index.php file, irrespective of the PHP file that I call from the browser. How can I debug this?

Docs Source

Here is my app.yaml file

 runtime: php81
    handlers:
    # Serve php scripts.
    - url: /(.+\.php)$
      script: \1
  

You're using php8 and GAE has a different way of handling it from php 5 (the document you referred to).

According to the documentation, you should either deploy a front controller to handle the routing or you code your index.php file to do that. The doc provided the following sample for using index.php

switch (@parse_url($_SERVER['REQUEST_URI'])['path']) {
    case '/':
        require 'homepage.php';
        break;
    case '/contact.php':
        require 'contact.php';
        break;
    default:
        http_response_code(404);
        exit('Not Found');
}