Website returned an error (Possibly 404 not found or other webserver error). Det

I have installed Cloudflare Flexible SSL on my site, and, as far as I know, it is working. However, when I go to the site https://www.whynopadlock.com/, I see the following with a big red X:

Website returned an error (Possibly 404 not found or other webserver error). Details:

(no details).

I also see the additional text:

*** NOTE ***: 0 items means no images were downloaded or existed on the page. It’s likely the URL you submitted was not a valid secure URL, or the page being tested only has text on it. Try copying and pasting the secure URL into a new browser window to make sure it displays as you’d expect.

Site does display ok, with https.

There are actually two images on the page I am testing.

I installed “SSL Insecure Content Fixer”. In the “SSL Tests”, there is the following:

Tests completed.

It looks like your server is behind a reverse proxy. The recommended setting for HTTPS detection is HTTP_X_FORWARDED_PROTO.

Your server environment shows this:

Array
(
[SHLVL] => 0
[PHP_FCGI_MAX_REQUESTS] => 5000
[REQUEST_SCHEME] => http
[LD_LIBRARY_PATH] => /usr/local/apache/lib
[HTTP_CF_CONNECTING_IP] => ip address here
[HTTP_DNT] => 1
[HTTP_CF_VISITOR] => {“scheme”:”https”}
[HTTP_X_FORWARDED_PROTO] => https
[HTTP_CF_RAY] => a number here
[HTTP_X_FORWARDED_FOR] => the ip address is here
[HTTP_CF_IPCOUNTRY] => US
)

I don’t think I can use SSL as long as I’m getting the error message on whynopadlock.com. So, I need to solve the problem. Is there anything you can see that needs to be corrected? Is the plugin message telling me there is something wrong? Thank you.