A fatal issue occurred during the DNS lookup process for cdkauffmannnextcloud.duckdns.org/A.
DNS response for cdkauffmannnextcloud.duckdns.org/A did not have an acceptable response code: SERVFAIL
A fatal issue occurred during the DNS lookup process for cdkauffmannnextcloud.duckdns.org/AAAA.
DNS response for cdkauffmannnextcloud.duckdns.org/AAAA did not have an acceptable response code: SERVFAIL
No valid A or AAAA records could be ultimately resolved for cdkauffmannnextcloud.duckdns.org. 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.