I am using cloudformation to create a lambda function with API integration and with custom domain name. I already have the necessary certificate setup completed (I am using Regional endpoint). My API has several routes like “payments”, “bdi” etc with a stage name called “test”. Below is my template.yaml.

MyApiGateway:
  Type: AWS::Serverless::Api
  Properties:
    AccessLogSetting:
      DestinationArn: !GetAtt MyLogGroupForApi.Arn
      Format: $context.extendedRequestId $context.identity.sourceIp 
      $context.identity.caller $context.identity.user [$context.requestTime] 
      "$context.httpMethod $context.resourcePath $context.protocol" $context.status 
      $context.responseLength $context.requestId
    Variables:
      stageName: test
    Domain:
      CertificateArn: !Ref Certificate
      DomainName: "uat-tests.int.coredev01.svc.com"
      Route53:
        HostedZoneId: !Ref HostedZoneId
    Name:
      !Sub
      - '${TheEnv}-${TheAppNameForResources}-api'
      - TheEnv: !Ref Environment
        TheAppNameForResources: !Ref AppNameForResources
        TheBucketRegion: !Ref AWS::Region
    TracingEnabled: true
    OpenApiVersion: 3.0.2
    Cors:
      AllowHeaders: "'Content-Type,X-Amz-Date,Authorization,X-Api-Key,X-Amz-Security- 

Token'”
AllowMethods: “‘‘”
AllowOrigin: “‘‘”
StageName: test
Auth:
ResourcePolicy:
CustomStatements:
– Effect: Allow
Principal: “*”
Action: “execute-api:Invoke”
Resource: “execute-api:/test/GET/payments”

APIDnsEntry:
  Type: AWS::Route53::RecordSet
  Properties:
    AliasTarget:
      DNSName: "uat-tests.int.coredev01.svc.com"
      EvaluateTargetHealth: false
      HostedZoneId: !Ref HostedZoneId
    Comment: !Sub 'DNS name for ${AppNameForResources} API'
    HostedZoneName: !Ref HostedZoneName
    Name: "ui-tests.int.coredev01.svc.com"
    Type: A

APIBasePathMapping:
  Type: AWS::ApiGateway::BasePathMapping
  Properties:
    DomainName: "uat-tests.int.coredev01.svc.com"
    RestApiId: !Ref MyApiGateway
    Stage: test

When CFN script is executed, I am getting this error pointing to APIBasePathMapping:

Resource handler returned message: "Invalid stage identifier specified (Service: 
ApiGateway, Status Code: 400

If I remove the APIBasePathMapping block, API is created successfully.
My goal is to create a custom domain endpoint for my API stage, so that I can refer the API without the wierd default API name created by AWS.

Not sure if I am missing anything else here?

Any help is much appreciated.