Hello, I have this problem, and i saw on other topics, that it was solved by . Please help me! 
We could not generate a cert for www.datii.pl because the required http-01 challenge failed. DNS problem: NXDOMAIN looking up A for www.datii.pl - check that a DNS record exists for this domain; no valid AAAA records found for www.datii.pl
The domain troubleshooting guide can help with most custom domain configuration issues. You might be able to use that guide to solve it before a human is available to help you. Then you can come back here and share the answer for bonus points.
https://vercel.com/docs/projects/domains/troubleshooting
You can also use v0 to narrow down the possibilities.
Hi , welcome to the Vercel Community!
Sorry that you faced this issue. I've fixed it manually from our end.
Happy shipping!