403 error while posting a particular string

Today, I am facing a weird problem.
I am getting 403 forbidden error while posting ajax data to a PHP file.
An error occurs for a specific string while posting via ajax call.

Error params and string

temp_name: Reminder (WITH OPTION TO confirm)

No error for the below string [same string without space before ( ]

temp_name: Reminder(WITH OPTION TO confirm)

If we remove the space before the open bracket, it’s working fine. Otherwise, it throws 403 forbidden as Ajax response.

403 Forbidden

In PHP, I am just getting the post value as

$temp_name=!empty($_POST['temp_name'])?$_POST['temp_name']:'';

Unable to find the cause of the error. Please suggest any idea to fix it.