title: Invalid type for parameter Message
body: <p>I try to use "signal" in Django to send SNS email in AWS and my code is:</p>
  
  <pre><code>import boto3
  from properties.models import PropertyList
  from django.db.models.signals import post_save, post_delete
  from django.dispatch import receiver
  
  @receiver(post_save, sender=PropertyList)
  def send_property_details(sender, instance, created, **kwargs):
      if created:
          sns = boto3.client('sns')
  
          response = sns.publish(
              TopicArn='',# I write value of TopicArn
              Message={
              "name": instance.title,
              "description": instance.description
                  },
              MessageStructure='json',
              Subject='New Property Created',
              MessageAttributes={
                  'default':{
                      'DataType':'String',
                      'StringValue':instance.title
                      }
                  },
              )
  
          print(response['MessageId'])
  </code></pre>
  
  <p>I get error as:</p>
  
  <blockquote>
    <p>Parameter validation failed: Invalid type for parameter Message,
    value: {'name': 'aws', 'description': 'test'}, type: ,
    valid types: </p>
  </blockquote>
  
  <p>In AWS docs said If I want to send different messages for each transport protocol, set the value of the <code>MessageStructure</code> parameter to JSON and use a JSON object for the Message parameter. What is wrong in my code?</p>
  
  <p><strong>Note</strong>: I want to send more than values so I need to send JSON </p>