It definitely looks like a DNS resolution issue. It might come from two places:
- Your local resolver (e.g. systemd-resolved)
- Your provider DNS
In the first case, you might try to restart the service and see if this helps (sometimes systemd-resolved is not happy with very low DNS TTLs):
sudo systemctl restart systemd-resolved.service
For the second case, this can be verified using dig. If you set dig to use a public DNS resolver (e.g. Google DNS 8.8.8.8) and it returns an answer (and not NXDOMAIN as in your comment), you can assume that your provider's DNS resolver is at fault.
For example, if I wanted to check test.ddns.net with the public DNS resolver 8.8.8.8, I could use:
dig @8.8.8.8 test.ddns.net
; <<>> DiG 9.16.33-RH <<>> @8.8.8.8 test.ddns.net
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 12144
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;test.ddns.net. IN A
;; ANSWER SECTION:
test.ddns.net. 60 IN A 109.162.33.40
;; Query time: 20 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Fri Mar 03 16:13:41 CET 2023
;; MSG SIZE rcvd: 58
In this case, it is important to note that:
- The status is: NOERROR
- I received an answer in the ANSWER SECTION that corresponds to the A record that I'm querying
If your provider's DNS is at fault, then you need to - at least temporarily - change your system DNS from systemd-resolved to a public one. Something like this might help.