Error: "This site can’t be reached"

Greetings,
After activating Cloudflare on my website, I recieve the error “This site can’t be reached” a lot of times when I try to open my website: classiom.com
I tried to solve it, but unfortunately I am not so familiar with the things in this context enough; hence, it would be appreciated if you can help me.
It is noteworthy to mention that I am not even sure about my DNS settings on Cloudflare, so I put its screenshop which may be helpful.
Thanks a lot,
Sincerely

I’m seeing a 521 error.

Your server is probably misconfigured. Probably something to do with its firewall.

I don’t really know what was the problem (regarding the 521 error), but I contacted the hosting provider and it is solved now.
So, may you kindly help me with the error that I described in my first message? Thanks a lot.

Is you message in accordance to 521 error? If it is, the error is solved now and I still need help for “this site cannot be reached error” which occures sometimes when I want to load the website (occures a lot).

Since it’s working now, it’s difficult to troubleshoot. Cloudflare will normally post an error code, which you didn’t list. But the first place to check would be server logs. You may need assistance from your host to look through server and firewall logs for the error event.

Are my DNS settings right?
When I see “this site cannot be reached”, there is no error code, only this message is shown in internet explorer app/software. I checked it with various devices and both ADSL/4G.
I saw the error in other topics on the forum, but those couldn’t solve my problem.

They must be, as your site is currently reachable.

I asked my host provider company. They said my DNS has problem.
In the DNS tab of Cloudflare, it shows a content of “136.243.24.110” for my website, but I don’t know actually what it is! I got these from intodns.com:

Nameserver records returned by the parent servers are:

tegan.ns.cloudflare.com. [‘173.245.58.226’] [TTL=172800]
derek.ns.cloudflare.com. [‘173.245.59.154’] [TTL=172800]

That’s why I have more doubts about my DNS settings.