Since you are getting 403 due to default GET servlet, this means that the URL is not mapping to a resource. It is possible the "provided navigation option" was generated wrong. It is possible the trailing / is to blame and could be checked first. Additionally see if the servlet (as a component) and the bundle are active.
There should not be a trailing slash while calling the Resource.
When Sling tries to resolve the same path, it won't be able to find the script to load. Please use any extensions .html, .json or .model.json etc. It will render the script based on extension or selectors match.