The 403 error is actually talking about the error document, not the original document. That's not a good sign as it means the server isn't set up properly.
Other than that - https://stackoverflow.com/questions/31365981/server-unable-to-read-htaccess-file-denying-access-to-be-safe
Other than that - https://stackoverflow.com/questions/31365981/server-unable-to-read-htaccess-file-denying-access-to-be-safe