Step::1 Login to your cPanel account and start searching for the File Manager icon under the FILES section.
Step::2 After opening the file manager click on public_html directory.
Step::3 Find the .htaccess file and right-click to Edit.
Step::4 After choosing an edit option, you see a popup asking to disable encoding if you wish. You have to click on the Edit button to continue.
Step::5 On a new tab, you can see many rewrite rules. You have to add the code to the .htaccess file.
<IfModule mod_security.c> SecFilterEngineOff SecFilterScanPOSTOff </IfModule>
Step::6 Save the file by clicking on the Save Changes button from the top-right corner of the screen.
Congratulations!! You have learnt how to Fix 406 or Not Acceptable error using .htaccess in cPanel