Requesting Solution Schema.org Validator “URL not found” – Server isn’t returning 200?

*Schema.org <http://schema.org/> Validator “URL not found” – Server isn’t
returning 200?*

I just tried validating my homepage with the Schema.org
<http://schema.org/> Validator
and received this error:

I’ve confirmed that:

   -

   The URL is entered correctly in the validator.
   -

   HTTPS is set up and serving pages.
   -

   Visiting the page in a browser loads it normally.
   -

   Running curl -I  against the URL returns 200 OK.

Yet the validator still can’t fetch the page. Has anyone encountered this
before? What might block the Schema.org Validator from recognizing a valid
200 response, and how can I fix it?
Kind Regards,
*MUSTAFA KHILJI*