包括joomla中的php文件在表中发布

I have php file (config) in this path joomla/includes and I need to include it with php codes in article page

these codes below doesn't work and not posting anything in the table

    <?php
if (isset($_POST['send'])) {

    require_once JPATH_BASE . '/includes/config.php';

$firstname = $_POST['firstname'];
$fathername = $_POST['fathername'];
$grandfathername = $_POST['grandfathername'];
$familyname = $_POST['familyname'];

$sql = "INSERT INTO subventions (firstname,fathername,grandfathername,familyname) VALUES 
('$firstname','$fathername','$grandfathername','$familyname')";

$inser = mysqli_query($con,$sql);

echo '<script type="text/javascript"> alert("sent"); </script>';

mysqli_close($inser); 
}
?>

I'm using third party plugin "Flexi Custom Code"

For security reasons you can't include custom code via editor.

So if you need to add custom code you can do this vía extension, one option is a plugin called Sourcerer, that allows you to add PHP, CSS, JS into joomla! content, including articles and modules. This may be a good option for you.