Manipulate contact form 7 data

I’m trying to manipulate the data sent in a contact form created by contact form 7.
Users select a product, which then sets a hidden text field with the value of all product id’s that are selected, separated from a comma.

I am trying to then change these ID’s to anhor links with the product’s title, all separated by a comma.

This is the code I have at the moment:

add_action('wpcf7_before_send_mail', 'my_wpcf7_before_send_mail');
function my_wpcf7_before_send_mail($form) {

    $submission = WPCF7_Submission::get_instance();
    $wpcf7 = WPCF7_ContactForm::get_current();

    if ($submission) {

        $data = $submission->get_posted_data();

        if (empty($data)) {
            return;
        }

        $extras = explode(',', $data['extras']);
        $extras_html = '';

        foreach ($extras as $extra) {

            if ($extra != '') {
                $extras_html .= '<a href="'.get_permalink(preg_replace('/s+/', '', $extra)).'">'.preg_replace('/s+/', '', $extra).'</a> ';
            }

        }

        $data['extras'] = $extras_html;

    }

    $wpcf7->set_properties(array(
        'mail' => $data
    ));

}

At the moment, the form simply fails to send.
All variations I have tried simply don’t manipulate the HTML.