SNS error - SMS "Rate exceeded" after 3 messages

Question

Hello,  
  
I am attempting to send SMS via SNS. Attempting to send 5 messages, 3 are received successfully but this error is returned and the 4th and 5th users do not receive the message:  
  
Error executing "SetSMSAttributes" on "https://sns.us-west-2.amazonaws.com"....  Sending SMS failed. Error message: Rate exceeded  
  
According to this page: https://docs.aws.amazon.com/general/latest/gr/sns.html , the limit is 900 transactions per second. I do not understand why I am getting this error at such a low level.  
  
The messages are very short. A second test had the exact same result (3 sent and then error).  
  
FYI using the PHP SDK.  
  
Please advise.

Answer

In case anyone has a similar problem.  
  
I was calling SetSMSAttributes and Publish on each request, to set the transaction type. However SetSMSAttributes has a much lower limit per second, and does not need to be called on each request for that purpose. Instead you can use MessageAttributes on the Publish request.  
  
'MessageAttributes' => \[  
                        'AWS.SNS.SMS.SMSType' => \[  
                            'DataType' => 'String',  
                            'StringValue' => 'Transactional'  
                        ]  
     
                    ],

SNS error - SMS "Rate exceeded" after 3 messages

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