Server is CentOS Linux release 7.9.2009 (Core), running Plesk Version 18.0.41 Update #1
Nginx as proxy, Apache as backend. My hosting provider is IONOS.
I have manually check the URL and my server shows the challenge, so my guess is that it is a networking issue: firewall, failures, etc. It is not clear to me if it is on my side or in Let's Encrypt side.
I have also checked fail2ban logs to make sure it is not blocking access from Let's Encrypt.
Nginx logs does not show the request from Let's Encrypt server too.
I have checked the status on Let's Encrypt and it shows all systems are up and running, but there was a maintenance activity yesterday.
Is your server listening on port 80 (http)? It is. It just takes a very long time to answer, occasionally.
I don't know what to attribute this delay to, if your server or your nameservers, or broken routing, DDoS on the internet infrastructure, or many other things.
I think you should just try again after a few hours (your client should, automatically).
The server is listening in port 80 and 443. In addition, if you copy and paste the failed URL in your browser, you can reach the file.
The problem is persisting, I have just received another report about timeouts trying to reach the server for renewing the certificate.
I had a closer look to the new report (here https://acme-v02.api.letsencrypt.org/acme/authz-v3/86877060220) and it is trying to connect to IPv6 addresses, but the server is not listening on them. I will remove the AAAA record and expect it will solve the issue.
I have also check if there is a firewall problem, but it isn't. See result of nmap from a different server outside of the cloud.novalido.es server.
[root@server ~]# nmap -p 443 cloud.novalido.es
Starting Nmap 6.40 ( http://nmap.org ) at 2022-03-12 18:14 CET
Nmap scan report for cloud.novalido.es (87.106.228.251)
Host is up (0.035s latency).
PORT STATE SERVICE
443/tcp open https
Nmap done: 1 IP address (1 host up) scanned in 0.66 seconds
[root@server ~]# nmap -p 80 cloud.novalido.es
Starting Nmap 6.40 ( http://nmap.org ) at 2022-03-12 18:14 CET
Nmap scan report for cloud.novalido.es (87.106.228.251)
Host is up (0.036s latency).
PORT STATE SERVICE
80/tcp open http
Nmap done: 1 IP address (1 host up) scanned in 0.61 seconds