title: SerializationException:Start of structure or map found where not expected: API Gateway to Step function
body: <p>I am using the standard blog tutorial on integrating api gateway with step functions from here:
  <a href="https://docs.aws.amazon.com/step-functions/latest/dg/tutorial-api-gateway.html" rel="noreferrer">https://docs.aws.amazon.com/step-functions/latest/dg/tutorial-api-gateway.html</a></p>
  
  <p>My step function expects the following output:</p>
  
  <pre><code>{
    "my_params": {
       "config": "config_value"
    }
  }
  </code></pre>
  
  <p>the Request body needed to do a post request as mentioned in the blog is:</p>
  
  <pre><code>{
   "input": "{}",
     "name": "MyExecution",
     "stateMachineArn": "arn:aws:states:us-east-1:123456789012:stateMachine:HelloWorld"
  }
  </code></pre>
  
  <p>I am passing my required input like this:</p>
  
  <pre><code>{
   "input": {
             "my_params": {
               "config": "config_value"
               }
            },
    "name": "MyExecution",
    "stateMachineArn": "my-arn"
  }
  </code></pre>
  
  <p>However, I am continuously getting following error:</p>
  
  <pre><code>{
  "__type": "com.amazon.coral.service#SerializationException",
    "Message": "Start of structure or map found where not expected."
  }
  </code></pre>
  
  <p>Can someone tell me what exactly is the problem here? What am I doing wrong here? Quick help appreciated.</p>