When attempting to create a Custom URL entry, you may receive the error message "The CNAME record for portal.acme.com does not point to acme.service-now.com".
The error message may be a result of any or a combination of the below issues.
1) There is no CNAME DNS record for your custom URL. If the below command does not return any results, then a CNAME record does not exist for your custom URL.
$ dig +nocmd +noall +answer -t CNAME portal.acme.com
2) Your custom URL has A record(s) configured. If the below command returns any results, then it indicates that you still have A record(s) configured for your custom URL.
$ dig +nocmd +noall +answer -t A portal.acme.com | grep -v "service-now.com"
3) The ServiceNow DNS servers used by the instance application nodes may still have the DNS records cached.
1) If your Custom URL does NOT have a CNAME record, then one needs to be created. Once created, your results should look similar to the below command.
$ dig +nocmd +noall +answer -t CNAME help.acme.com
help.acme.com. 11168 IN CNAME acme.service-now.com.
2) If your Custom URL still has A record(s), these will need to be removed. Once removed, the below command should not return any results.
$ dig +nocmd +noall +answer -t A help.acme.com | grep -v CNAME | help.acme.com
3) DNS record updates will take time to propagate through the internet which depends on the TTL value. Please allow some time for the DNS records to expire on the ServiceNow DNS Servers, then try to create the Custom URL again.