I believe you already have a value added for the custom domain which is why you’re unable to add the CName. Please try editing the existing record for the custom domain with the values below and you should be able to validate your domain.
I have had a session with AWS support and they have given the opinion that it can’t be done Quote " CNAME records cannot co-exist with any other record e.g. A, NS, SOA, TXT [1], this will prevent the successful creation of a CNAME record on the zone apex e.g. “example.com” or in the subdomain (record) such as “sub.example.com”, if there are other records present."
Im sure we cant be the only ones in the world with this issue and there must be another way to validate the domain. I would have thought that the TXT record alone would show control over the domain and is the way google does this.
Yes, you are right there. CNAME records cannot co-exist with any other records for a domain but if you check the attached screenshot from my previous response, all of the records: A, NS, SOA, and TXT are for the domain (example.com) and only one record exists for subdomain (sub.example.com) which is CNAME. Try similarly setting your records and that should resolve this.
In any case, if you’re still unable to set it - please write to us at [email protected] with the screenshots and we will help you set this up.