params =   {TargetArn: 'arn:aws:sns:us-east-1:.../.....f',MessageStructure: 'json',message: 'hello' }
sns.publish(params);

/var/lib/gems/1.9.1/gems/aws-sdk-core-2.0.34/lib/seahorse/client/param_validator.rb:24:in `validate!': parameter validator found 2 errors: (ArgumentError)
  - unexpected value at params[:TargetArn]
  - unexpected value at params[:MessageStructure]