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I use Koivi with SmartSection 2.13/xoops 2.0.18 and got it working by following this FAQ:
https://xoops.org/modules/smartfaq/faq.php?faqid=591
It really is as easy as adding the /wysiwyg folder to the xoops_root/class folder and selecting "KoivI" in the module's preferences. No need to install anything or upload any other folders.
I assume it works with the other wysiwyg editors, but I haven't tried it myself.
HTH