No valid A or AAAA records could be ultimately resolved for network-fail.foo.monkas.xyz. This means that Let's Encrypt would not be able to to connect to your domain to perform HTTP validation, since it would not know where to connect to.
No A or AAAA records found.
The IANA public suffix is the TLD of the Registered Domain
The TLD for network-fail.foo.monkas.xyz is: xyz