FranciscoAMK

Just put the “wc-dineromail” folder into the plugin’s root folder, then activate the plugin from the wordpress admin.

That may work.

Oh sorry. So, the question is: Where do I have to put this line into woocommerce.php?

include( 'classes/gateways/dineromail/class-wc-dineromail.php' );

I did this and worked very well for me. The only problem is that you have to save the post an then the meta box appear.

$post_id = $_GET['post'] ? $_GET['post'] : $_POST['post_ID'];
$template_file = get_post_meta($post_id, '_wp_page_template', TRUE);

if ($template_file == 'template-quienessomos.php') {
    ot_register_meta_box( $quienessomos_meta_box );
}