Get Arn for Resources build by Plugin

Serverless Framework
1

I’m using two serverless plugins (serverless-fargate, serverless-step-functions) with the basic idea of having my step function start a task in a fargate cluster. I’m able to spin both up but I’m not clear how reference the fargate cluster and task in the state definition.

fargate:
  clusterName: price-cluster
  vpc:
    securityGroupIds:
      - !Ref LambdaSecurityGroup
    subnetIds:
      - ${self:custom.config.${sls:stage}.vpc.subnet1}
      - ${self:custom.config.${sls:stage}.vpc.subnet2}
  tasks:
    download-test:
      image: appImage
      environment:
        file_path: test.py
      service:
        desiredCount: 0

my first thought was to use the alias because I have done with lambda functions before eg

functions:
  downloader:
    handler: scarper.main
    description: ${self:custom.config.appName} ${sls:stage} lambda downloader
    layers:
      - !Ref PythonRequirementsLambdaLayer
.....

          In-Network-Parser:
            Type: Task
            Resource: !GetAtt inNetworkParser.Arn
            End: true

but when I tried Cluster: !GetAtt fargate.Arn I got The CloudFormation template is invalid: Template error: instance of Fn::GetAtt references undefined resource fargate

I was tried using ${self:fargate} but that just gave me an object.

I guess this is a long way to ask how to reference the Arn for this plugin resource.