Test the two hostnames separately
Test www as its own DNS name, host binding and TLS name; fix the layer shown by the error.
example.com and www.example.com need separate DNS, host binding and TLS checks. Record whether www fails to resolve, serves the wrong site, warns about its certificate or loops through redirects. This is a www repair after the root works, not a whole-zone move.
Ask the web host what www target and redirect policy it supports. Do not assume www should always be a CNAME to the apex: a proxy, CDN or application provider may supply a different target.
Compare public DNS answers
Run dig example.com A +short, dig www.example.com A +short and the same queries for AAAA and CNAME. Query an actual delegated nameserver directly if results disagree. A missing www answer calls for a record at the authoritative provider. A record to an old IP calls for a corrected target. If www is a CNAME, follow its destination and check that it resolves. Do not add an A beside a CNAME at the same name. Check whether the panel appended the domain twice to a full name.
Distinguish NXDOMAIN from SERVFAIL: NXDOMAIN can mean the name is absent; SERVFAIL may point to a nameserver or DNSSEC problem. If only one resolver shows an old answer, check the previous TTL before editing again. A wildcard record can make www resolve even without an explicit entry, but its target may be wrong.
Check host binding, redirect and certificate
If DNS resolves to the intended service but www shows the wrong site, ask the host whether the www hostname is attached to the correct application or virtual host. Test an HTTP response and inspect its redirect Location header. If HTTPS warns about a name mismatch, the certificate must cover www as well as the root; a DNS change alone cannot add a certificate name. If the certificate request fails, use the related TLS guide and inspect the exact validation error.
Decide which hostname should be canonical with the application owner. The other may redirect, but avoid conflicting redirects at the panel, application and proxy layers. A loop is an HTTP configuration fault once DNS and TLS reach the host; the related redirect-loop guide handles it.
Change one verified cause
If www lacks DNS, publish the host-supplied A, AAAA or CNAME at the live authority. If the record is right but the host binding is absent, add or request the www alias through the account’s supported interface. If TLS is the only failure, request coverage for www after validation prerequisites pass. Save the old setting and modify one layer at a time. Do not change nameservers, MX or unrelated TXT records for a www-only repair.
If www.example.com resolves correctly but HTTPS reports a certificate-name mismatch, leave its DNS record alone and request certificate coverage for that hostname.
After each step, query the authoritative answer, then test http://www.example.com/ and https://www.example.com/ with redirects visible. Verify the final content and certificate name, and confirm the root domain still works. Cached old DNS can persist until its TTL expires.
Recover and escalate
If a new record points visitors away from the site, restore its saved value and confirm at the authoritative server. If a redirect change creates a loop, revert that one change and capture the Location sequence. Ask support for help with the exact hostname, record answers, HTTP status/Location sequence and certificate error. Do not send panel credentials.
Common questions
Should www point to the same IP as the root? Follow the hosting provider’s instruction; some services use a distinct alias.
Can one certificate cover both names? Yes if both names are included, but check the issued certificate.
Will fixing www affect email? A change limited to www web records should not alter the apex MX, but preserve all unrelated records.
Does a DNS answer guarantee www works over HTTPS? No. The host must serve that name and its certificate must cover it.
Sources and technical references
Related guides
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