Cloudformation on Api Gateway DomainName Failure

AWSTemplateFormatVersion: "2010-09-09"
Description: Descrixxxxxxxxxxxxx
Resources:
  myDomain:
    Type: AWS::ApiGatewayV2::DomainName
    Properties: 
      DomainName: feature-notifications-ws.tecxxxxxxxxxxxns.com
      DomainNameConfigurations:
        - EndpointType: REGIONAL
          CertificateArn: arn:aws:acm:eu-west-1:xxxxxxxxxxxx:certificate/xxxxxxxx-cab2-48e1-bf95-xxxxxxxxxxxx
Outputs:
  routeTest:
    Description: Text random than describes....
    Export: 
      Name: feature-notifications-test
    Value:
      !GetAtt myDomain.RegionalDomainName

References to RegionalDomainName or RegionalHostedZoneId causes "Internal Failure".