How do I solve “default backend - 404” error problem? The error came up after I pointed my DNS to Cloudflare.
Make sure you have a valid SSL certificate on your server.
But that’s why I came to Cloudflare. All I want is for my site to show https:// instead of http://. Can you help in this direction?
Then you have come the wrong way I am afraid 
You still need a certificate on your server in any way.
No! I’ve done this before and everything was perfect but suddenly, the site started developing issues. Why did it work the first time? What’s happening now?
What more? My friend is on a secured connection courtesy of Cloudflare free SSL plan. Please, think of something. I trust that you can help. Maybe I’m not getting something quite right.
Not again that discussion, please. We had that a million times.
Just install a certificate on your server and the issue most likely is fixed. It is not like these certificates cost the outrageous amount of $10 a year anymore 
. Either get a Lets Encrypt certificate or Cloudflare Origin one. Choice is yours.
Oh! We are getting there. I said you can do something and you are very close there. I love the sound of Cloudflare Origin. How do I get started with that?
A search engine would always be a good start
But that certificate really is not much different from LE for example, with the difference that you can choose a longer validity period and renewal is easier, however it is only valid in a proxied context and not accepted by e.g. browsers.