title: How to concatenate constant string with jsonpath
body: <p>I have AWS step machine and one of the step is used to notify failure using SNS service. I want to select some metadata from <code>input</code> json into outgoing message. So i am trying to concatenate constant string with jsonpath like below</p>
  
  <pre><code>"Notify Failure": {
        "Type": "Task",
        "Resource": "arn:aws:states:::sns:publish",
        "Parameters": {
          "Message.$": "A job submitted through Step Functions failed for document id $.document_id",
          "Subject":"Job failed",
          "TopicArn": "arn:aws:sns:us-west-2:xxxxxxx:xxxxxxxx"
        },
        "End": true
      }
  </code></pre>
  
  <p>where <code>document_id</code> is one of the property in input json</p>
  
  <p>However when i try save state machine defination i get error</p>
  
  <blockquote>
    <p>There is a problem with your ASL definition, please review it and try
    again The value for the field 'Message.$' must be a valid JSONPath</p>
  </blockquote>