1. Go to this page and download the library: Download stereo/contact-form library. Choose the download type require.
2. Extract the ZIP file and open the index.php.
3. Add this code to the index.php.
<?php
require_once('vendor/autoload.php');
/* Start to develop here. Best regards https://php-download.com/ */
add_action('st_cf_files',function($files,$postid) {
foreach($files as $f) {
// $f is a temp file path that will be deleted after this hook.
}
}, 10, 2);