cant save changes to email templates

-- HikaShop version -- : 4.2.1
-- Joomla version -- : 3.9.10
-- PHP version -- : 7.1.14
-- Browser(s) name and version -- : CRHOME 75.0.3770.142
-- Error-message(debug-mod must be tuned on) -- : Trying to save a change on the Order creation notification email and I get this error:

Not Implemented
GET to /administrator/index.php not supported.
Additionally, a 501 Not Implemented error was encountered while trying to use an ErrorDocument to handle the request.

Apache Server at www.kaleidoscopeuniforms.com Port 443

Trying to save a change on the Order creation notification email and I get this error:

Not Implemented
GET to /administrator/index.php not supported.
Additionally, a 501 Not Implemented error was encountered while trying to use an ErrorDocument to handle the request.

Apache Server at www.kaleidoscopeuniforms.com Port 443

Hi,

This means that you probably have a security system on your website / web server which prevents the saving as it flags it as potentially harmful.
www.hikashop.com/forum/orders-management...l-customisation.html
www.hikashop.com/forum/orders-management...when-save-email.html