Redsys is a popular payment gateway. It has extensions for many e-commerce solutions like WooCommerce, PrestaShop, Magento, etc.
Currently it does not support the Let's Encrypt Certificate Authority and SNI. However, we support other options for the successful usage of the Redsys payment gateway.
First, the communication between the website and the Redsys payment gateway can be managed over HTTP (without an SSL certificate). Another option is to purchase a Wildcard SSL or an EV SSL certificate from the User Area->Add Services section. It comes with a dedicated IP and is issued by Globalsign. A dedicated IP will also be assigned to your account if you order the installation of an external SSL certificate in case you already have one.