I recently have been running a server for a friend and have been getting alot of 403 Forbidden errors.
This usually means that the user is not able to access the content. For the most part you can try to assign permissions to the user “www-data” to the webroot. Here is an official description:
403 Forbidden errors are Nginx’s way of telling “You have requested for a resource but we cannot give it to you.” 403 Forbidden is technically not an error but a HTTP status code.