@Ravi_Prabhakar in trying to provide better answer can you share what isn't clear on this Help Topic of yours Can we generate the SSL certificate without any domain? that meant you needed ask for the Help of this Topic?
I do believe some critical small nugget of missing information is the issue at hand, I am trying to learn to see what small gems of information that the OP needs in a fashion to better help.
Let’s Encrypt offers Domain Validation (DV) certificates.
Thus you need to own and have control over the Domain Name (or have a subdomain under an existing domain name, for example pointed to your server by your employer or school) you wish to obtain a certificate for, from an ICANN Accredited Registrar.
For Let’s Encrypt to issue a Domain Validation (DV) certificate Domain Validation must happen
and it is a CA/Browser Forum Baseline Requirement.
Let's Encrypt uses Multi-Perspective Validation Improves Domain Validation Security - Let's Encrypt
Since these are Domain Validation (DV) certificates the Domain Name System (DNS) is used extensively in the validation process as well a allowing us to assist here on Let's Encrypt community.
DNS Queries need to give consistent results from any location on the Internet, all your authoritative DNS Servers for the Domain need to also give consistent results as well.