Forbidden - Access to the requested file is forbidden - Textarea

Hello, I am getting this error after entering text is textarea.
1.!!! The error does NOT occur when I only enter text;

2. I get an error when I try to format the text / centered, change color, etc. /
3. The error also occurs in "HTML editing" mode in Textarea.

In this case I get the error : <p style="text-align: center; "><b>hello</b></p>

but in this case NOT: <p><b><a href="google.com">hello</a></b></p>

Error can be seen when trying to add or edit Slider.

LiteCart v2.5

This sounds like a false positive firewall block commonly caused by Imunify360 and mod_security.
Contact the web host and let them know the exact time and URL where this occured for them to adjust this firewall rule.

Hello again. Actually the problem was at the server level and it came from mod_security. After it was turned off, everything worked fine.
Thank you for your help too.

Isn't that what I said? mod_security

Yes exactly.