Troubleshooting
Domain is not resolving
Nameservers, records, TTL and the wrong host.
Authoritative DNS
Look up the nameservers at the registry. If they are not the hosts you think, your A record elsewhere is ignored. Align nameservers with where you edit records.
The record
Confirm an A (and AAAA if you use IPv6) for the hostname visitors type, including www vs apex. CNAME cannot sit on the apex. Wait for TTL; a 86400-second record will not flip in five minutes.
The server
The IP in DNS must be the VPS or host that is actually serving HTTP. After a reinstall or a new VPS, update the A record. Check the host firewall allows 80 and 443.