What is the difference between HTTP DCV and DNS DCV?
DCV stands for Domain Control Validation. This is used with AutoSSL to validate the domain in order for the certificate to be issued to the requested domain. There are two DCV methods, HTTP and DNS. The domain is validated if either of the DCV methods succeeds.
The HTTP DCV method attempts to verify your domain by querying a text file on the site and comparing the content of the text file to an MD5 hash of the CSR. The text file is located in the domain's .well-known/pki-validation/ folder for the Let's Encrypt provider. The text file is located in the domain's .well-known/acme-challenge/ folder for the Sectigo provider.
The DNS DCV method attempts to verify your domain by adding a DNS record to your domain's DNS zone. A TXT record is added for the Let's Encrypt provider. A CNAME record is added for the Sectigo provider.
Please note that if your domain's DNS is not managed in the cPanel & WHM server where it is hosted, the DNS DCV will fail. This is the expected behavior since it won't be possible for the cPanel & WHM server to modify your DNS records if they are hosted elsewhere.