Wordpress - Moodle Subscription integration with RedSys

There is a running wordpress site and moodle one, and a shared mariadb database. It is needed to implement a way to sell course subscriptions from the wordpress site using the RedSys payment gateway. They provide these tools: https://pagosonline.redsys.es/descargas.html.

Note: If any third-party plugin/library/tool must be used, it needs to be either free or open-source. No additional charges.