Domain Name System Security Extensions (DNSSEC) is a security protocol that authenticates DNS records, verifying the data has not been modified during retrieval from its authoritative name server. 

You may not have DNSSEC enabled on your server as it is an optional protocol. If DNSSEC is present, though, a Certificate Authority is required to validate the signature during the domain validation process for certificates (including SSL and S/MIME). 

If there are any errors in your existing DNSSEC configuration, validation will fail, and the certificate will not issue. 

Please check with your DNS manager or server/system administrator to resolve potential issues with DNSSEC. Our support team is not able to troubleshoot DNSSEC. 

Read more: Sectigo Reference Guide: DNSSEC and Certificate Issuance