DNS/awsdns/APIについて、ここに記述してください。

ConflictingDomainExists

    The cause of this error depends on whether you're trying to create a public or a private hosted zone: 

Public hosted zone: 

Two hosted zones that have the same name or that have a parent/child relationship (example.com and test.example.com) can't have any common name servers. 

You tried to create a hosted zone that has the same name as an existing hosted zone or that's the parent or child of an existing hosted zone, and you specified a delegation set that shares one or more name servers with the existing hosted zone.

 For more information, see CreateReusableDelegationSet. 

https://docs.aws.amazon.com/Route53/latest/APIReference/API_CreateReusableDelegationSet.html

Creates a delegation set (a group of four name servers) that can be reused by multiple hosted zones.

If a hosted zoned ID is specified, CreateReusableDelegationSet marks the delegation set associated with that zone as reusable.

Note

You can't associate a reusable delegation set with a private hosted zone.