this domain name has the ip address
nslookup guest-wifi.hreuk.com.
Name: guest-wifi.hreuk.com
Address: 10.1.2.1
But 10.1.2.1 is a private ip address, not public. It isn't possible to connect this server.
Perhaps you want to use dns-01 - challenge, then you can create a certificate. But I don't know if the Acme Certificate plugin supports that.