What is DNS DCV and HTTP DCV? What is the difference?
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 2 types of DCV; DNS & HTTP.
DNS DCV attempts to verify your domain by adding a DNS record to your domain's DNS zone (either a TXT for Let's Encrypt or CNAME for Sectigo record).
If your domain's DNS is not managed in the cPanel & WHM server where it is hosted then DNS DCV will fail. This is nothing to worry about as this is normal and intended behaviour based on that setup since it won't be possible for the cPanel & WHM server to modify your DNS records if they are hosted elsewhere.
HTTP DCV is the method used to verify a domain by placing a file in the following path of the domain:
http://domain.tld/.well-known/pki-validation/<$MD5 has of CSR>.txt
http://domain.tld/.well-known/acme-challenge/<$MD5 has of CSR>.txt
The file name is the MD5 hash of the CSR used for the certificate and is created as a plain text file which AutoSSL will then try to reach. If the file is able to be successfully reached, then validation will pass.
Sometimes, redirects, htaccess restrictions, or even alternative web-servers may interfere with this and prevent AutoSSL from completing HTTP validation.