AWS SNS - SMS not receive to mobile at some times

To understand what is going wrong we have to understand how SMS ecosystem works in Amazon SNS.

When we publish SMS text messages to Amazon SNS, it hands over the SMS text message to a third party aggregator. This aggregator would then contact the corresponding mobile carrier to which the destination number belongs to. The destination mobile carrier would then deliver the SMS text message to the end device (mobile phone).

Depending on the status of the SMS text message, the mobile carrier would generate a status message called "Delivery Report" and send that over to the aggregator. The aggregator would in turn send that delivery report back to SNS which shows up as SNS SMS delivery status logs in your CloudWatch log group(s).

Now, the status message "Message has been accepted by phone carrier" means that the mobile carrier has successfully accepted the SMS text message from AWS via the aggregators and will attempt the SMS text delivery. This delivery status log message usually does not mean that the SMS text message has been successfully delivered to the end device.

To further troubleshoot SMS delivery issues like this, you have to engage the aggregators and the mobile carriers. To engage them, please reach out to AWS Support and provide them with the SMS message IDs from your CloudWatch log group. Please ensure that these message IDs are not older than 72 hours. This is because, majority of the telecom operators and the AWS aggregators do not hold on to message IDs and their details for more than 3 days.

AWS Support team should be able to engage the aggregators and the mobile carriers in Sri Lanka to further troubleshoot the issue.

I hope this helps.