The files of your site look fine, so it’s possible the problem is somewhere else.
I see you’re using Cloudflare on your domain. Can you please check Cloudflare’s DNS settings? Your domain should point to the “Website IP” displayed in the client area. If it’s pointed somewhere else, that may cause your site to show this error as well.
Attached above, I have listed my DNS settings. The ones highlighted in blue match the “website IP” displayed in my client area, while the ones in red are different. Do I delete the ones in red or change anything?
Pointing your domain to a different domain will result in clients being connected to the wrong IP address, leading to a host of undesirable results.
And even if you want a Let’s Encrypt or ZeroSSL certificate while using Cloudflare, having the _acme-challenge record with Cloudflare proxy enabled will not work for verification.