-Check file permissions
First, you need to check the file permissions that each of your files has set. If a file or folder is set to “777” which is “world” writable for security reasons the 403 error will be displayed to protect your website from hacks. Folders should have the permissions set to “750” or “755” and files should be set to “644”.
If you have SSH Access, you can resolve this easily. Make sure you’re in the root directory of your Magento installation, and then execute the commands.
If this will not work then you can check 'promo_catalog/newConditionHtml" is overriden anywhere in your code, local.
Also,
Check “No Index” in .htaccess file
Once you have verified that all the permissions are correct but the issue still persists, you will need to check your .htaccess file. Keep in mind that you can have multiple .htaccess files in your account, so you may need to search / modify .htaccess files other than public_html/.htaccess. For example, if you have an addon domain located at public_html/addon_domain, you’ll need to check any .htaccess files within that folder as well. If one of the lines in the actual file says “Options All -Indexes” then simply remove “-Indexes” and save the file.