Description
For configuring ServiceNow custom URL one of the basic requirements is to create a CNAME on the DNS that points to the instance.
Creating the CNAME is failing with "Cannot create CNAME record at the APEX domain"
Cause
CNAME cannot be created at the root/apex of a domain, for example: myservicenow.com
Resolution
As seen in the documentation the customurl should be of the format servicenow.acme.com and not acme.com, the fully qualified domain name (FQDN) of the custom URL.
Note: For example, servicenow.acme.com is the FQDN of the https://servicenow.acme.com URL.