Cannot Update Emails

-- HikaShop version -- : 4.7.3
-- Joomla version -- : 4.3.2
-- PHP version -- : 8.2
-- Browser(s) name and version -- : Firefox 113.0.2
-- Error-message(debug-mod must be tuned on) -- : Not Implemented

POST not supported for current URL.

When trying to update system emails or even clicking on the Cancel button, I get a "Not Implemented POST not supported for current URL." error. I have had to download the applicable files, make my edits (in the "modified" files) and then FTP them back up. This affects "Order administrator notification", "Order creation notification", and many others. Though, it does not affect some of the others.

I do have the RSFirewall plugin installed on the site. However, that is not set to scan the administrator section, only the front end.

It is rather strange that this error happens with some of the emails, but not all. I've worked around the issue, but it would be much easier to maintain those emails through the admin UI.

Even when disabling that extension entirely, that problem still persists.