Mapping to Domain
Domain mapping has been rolled out for personal sites. See Steegle's information.
For domains registered with Google Domains click here.
Note: This website is now mapped to: https://new.k8oms.net/ and https://www.k8oms.net/
If you want a domain link that goes to a particular page in your site, use forwarding instead of mapping. For instance rate.k8oms.net
I did this by setting up forwarding in my domain panel to forward the subdomain 'rate' to a page in the site.
New Google sites are automatically secure (https) at the native Google URL and at the mapped domain, so it is not necessary to purchase a SSL certificate. If necessary, use this procedure to refresh the certificate: Remove the custom URL from your site, wait about 15 minutes then add the custom URL again and that will generate a new SSL certificate.