Check the Domain Name Severs (DNS)

Please read this article first. Afterwards, google .suffix WHOIS lookup online. suffix is your domain’s suffix. For example, if you are using a .xyz domain, then search .xyz WHOIS looup. In this example, you can directly go to this eurodns website to check your .xyz domain’s DNS.

Set the Custom Domain for Github Pages

First, go to your github page repository, go to Settings->Pages and fill in your custom domain name
Notice the domain name is without www.

Second, set custom resource records for the domain. Specifically, you have to set A and CNAME records for the selected domain.

• A record.

  Make an A record pointing to 185.199.108.153, 185.199.109.153, 185.199.110.153 and 185.199.111.153
  

  The IP addresses are required to use the free HTTPS support for GitHub pages.

• CNAME record

  To redirect www subdomain to the github domain, add a CNAME record with your GitHub pages profile URL. That is:
  

For more information, check the github official documentation of how to manage a custom domain.

Troubleshooting

• Github pages support https for both www and apex domains