I’ve fixed a bug where if the SHA256 test field was used, it would give an error in the gateway. This has been due to an error on my part where I forgot to modify a part of the code. Real orders were not affected by this problem.
If you don’t have it installed, you can download it from WordPress.org, and I recommend that you look at the page on the differences between Redsys’ free WordPress.org Plugin and WooCommerce.com’s premium Plugin, you will surely be surprised.