SMS is being delivered multiple times

Question

  • Why has my SMS been delivered multiple times?
  • How can I stop my message being sent repeatedly?
  • Have you sent my SMS more than once?

Context

Very occasionally you can make a single API call and the message can arrive several times at the handset.

Answer

At Nexmo we do not generate retries from our platform, and we only pass one copy of each message to the suppliers for each API call.

The two most common reasons for multiple deliveries are:

1. Non-communication of the initial response from the handset on the first attempt at delivery by the supplier. When no response is received this triggers retries on the SMSC level of our operator-partner. As you have noticed the delivery is duplicated we can conclude that the handset actually did receive the submissions but the acknowledgement failed to reach the SMSC. This will most likely have been caused by a communication error in an inter-operator signalling level, which in rare cases may result in multiple delivery.

2. Duplicate API calls being sent by your platforms to us. We pass on as many requests to our suppliers as we receive in API calls, so if multiple API calls are sent due to an error or a loop in your system, we will send the same number of SMS to our suppliers for you.

This issue can usually be solved by restarting the handset. If this does not work, please contact us at support@nexmo.com for further assistance.

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