It produced this output:
Select the appropriate numbers separated by commas and/or spaces, or leave input
blank to select all options shown (Enter 'c' to cancel):
Requesting a certificate for in-vse.cz
Performing the following challenges:
http-01 challenge for in-vse.cz
Waiting for verification...
Challenge failed for domain in-vse.cz
http-01 challenge for in-vse.cz
Cleaning up challenges
Some challenges have failed.
To fix these errors, please make sure that your domain name was
entered correctly and the DNS A/AAAA record(s) for that domain
contain(s) the right IP address.
My web server is (include version): Apache/2.4.41 (Ubuntu)
The operating system my web server runs on is (include version): Ubuntu 20.04
My hosting provider, if applicable, is: active24.cz
I can login to a root shell on my machine (yes or no, or I don't know): Y
I'm using a control panel to manage my site (no, or provide the name and version of the control panel):
The version of my client is (e.g. output of certbot --version or certbot-auto --version if you're using Certbot): certbot 1.14.0
I currently see it set to 2002:515f:6c39::515f:6c39, but there is no server available at that IPv6 address. Can you check with your hosting provider to confirm that this is your correct IPv6 address?
Thanks for sharing your solution. I want to point out for other readers that not all sites will use this kind of conversion mechanism. In many cases, you would be issued an IPv6 address directly by your hosting provider, which could be completely independent of your IPv4 address.
I wouldn't use these kinds of "converted" IPv6 addresses if I were you. The method used by that site is 6to4 which is just a transitional mechanism until native IPv6 was properly deployed. Nowadays, anno 2021, this should be the case and one should not fall back on mechanisms such as 6to4..
As an example: I can't connect to your IPv6 address at all:
osiris@erazer ~ $ traceroute 2002:515f:6c39::515f:6c39
traceroute to 2002:515f:6c39::515f:6c39 (2002:515f:6c39::515f:6c39), 30 hops max, 80 byte packets
1 2001:xxxx (2001:xxxx) 4.608 ms 4.548 ms 6.019 ms
2 xx.yy.zz.xs4all.net (2001:888:1:xxxx::1) 16.527 ms 18.598 ms 18.588 ms
3 0.ae23.xr4.1d12.xs4all.net (2001:888:1:4034::1) 23.372 ms !N 23.946 ms !N 13.284 ms !N
osiris@erazer ~ $
As you can see, a router of my ISP is refusing to route the traceroute any further..
