Github 客服的回复如下，遇到一样问题的可以参考下：


Hello,

Thanks for writing in! I took a look and it appears that your custom domain is set up using a CNAME record. You'll need to make some changes to your DNS settings before we'll be able to renew the HTTPS certificate for your custom domain.

You'll need to remove your existing CNAME record, and replace it with at least one A record that points to one of the following IP addresses:

185.199.108.153
185.199.109.153
185.199.110.153
185.199.111.153
Optionally, you can create additional A records that point to the other IP addresses from the list. Additional records essentially act as a backup in case of DNS or CDN issues, so having at least two is best practice, though your site will still function with just one.

Once you've replaced the CNAME record, you'll need to visit your repository's settings page, remove your custom domain and click save, then re-add it again. This will kick off the process of provisioning an HTTPS certificate for your domain name.

Once your certificate has been provisioned, you'll then be able to enforce HTTPS by checking the "Enforce HTTPS" checkbox.

Bear in mind that it can take up for 24 hours for DNS changes to take full effect, and up to an hour for an HTTPS certificate to be requested, so if you follow these steps but are still having trouble, that's usually why.

Cheers,
Steven