Woocommerce Email attachments not working – file not being attached

Apparently Woocommerce need a local path and not a URL to the file. In order to fix I used this:

function attach_order_notice ( $attachments, $email_id, $order ) {
    // Only for "New Order" email notification (for admin)

    //if( $email_id == 'new_order' ){
        $file_path = wp_upload_dir()['path'];
        $file_name = get_field( 'email_file_attachment', 'options' )['filename'];
        $attachments[] = $file_path . "https://wordpress.stackexchange.com/" . $file_name;
    //}
    return $attachments;
}
add_filter( 'woocommerce_email_attachments', 'attach_order_notice', 10, 3 );

I hope this helps someone.