Redsys is the Servired / Sermepa successor. It is the leader of spanish online payment gateways with 88% market share.
The plugin integrates K2Store with Redsys. To use this payment gateway, you will need to contract with your bank and the Redsys Gateway.
The plugin supports banks including - La Caixa, Banco Sabadell, Caixa Penedes, Caja Rural, Unnim, Deutsche Bank.
Full list can be read from here: http://www.servired.es/espanol/miembros.htm
The plugin comes with a Documentation PDF, which you can download after purchasing the plugin and then going to My Account -> My Downloads