Was your domain possibly earlier with some other provider who used Cloudflare as well? In that case, some settings might be stuck and you might have to contact support so that they manually fix that.
What’s the domain? And would you feel comfortable sharing the IP address?
In that case you’d have a Lets Encrypt certificate on your server but it’s not valid for that hostname and should not load when paused either. You’ll need to configure a valid certificate, the 526 is to be expected for now.
Alternatively you could also check out Cloudflare’s Origin certificates. They can be issued from the SSL screen. Only keep in mind, Origin certificates are only valid in proxied contexts, you won’t be able to unproxy the site.
As I already said yesterday, you appear to have a broken certificate and need to fix that. As I also already said you best pause Cloudflare (or set the record to unproxied) and fix the certificate and only then proxy again.
Thanks. I pause Cloudflare and disable proxy. When entering URL calibre.chotechai.com, and check the certificate information. The certificate was issued for another domain of mine, instead of for chotechai.com. It is strange because when I enter chotechai.com (Cloudflare is active and proxied, ssl=full,strict), it works fine with the right certificate without error.My Apache config for chotechai.com is pointing to the right certificate keys.
FYI, both bthofen.com and chotechai.com are hosted on a same server at home with a single public IP. Ubuntu 18.04, Apache2
Thanks. I found the cause of error. I generated let’s encrypt for chotechai.com separately from my main domain xxxx.com.
Solution: I have to generate only one, and same, let’s encrypt certificate for both xxxx.com and chotechai.com.