Here are the most common causes of 403 errors:
1 - Mod Security has blocked access to the page due to a rule infringement
Mod security is a system that filters all incoming requests to your website. It works in the background, and checks every page request against thousands of rules
2 - Incorrect file permissions
In order for the world to be able to browse your website, you have to give it permission! This is usually all handled automatically when you upload files. However, if you have been working with permissions, then it's possible you made a mistake.
Please ask your hosting provider to help you