How is that relevant?
It seems as if you didn’t not use the search, which would have been a good idea as you’d have come across Community Tip - Fixing Error 521: Web server is down
Anyhow, as the error is pretty clear about, your server is not reachable. Assuming your server IP address ends in 161, it simply would appear your server is not configured for HTTPS. Make sure it is and that it has a valid certicate and you should be good to go.