Troubleshooting undelivered SMS messages sent from a Hologram device

Hologram SIMs are designed for global IoT communication and are generally considered to be non-domestic devices by local carriers. This can be an issue when it comes to delivering Short Message Service (SMS) messages. SMS messages marked as delivered indicates that Hologram has delivered the SMS messages to the receiving device's network. However, this does not guarantee that the receiving network will successfully deliver the SMS message to the end-device.

Please note that Hologram charges for attempt of delivery. If Hologram successfully sent the SMS messages, the SMS charge will be incurred even if the end device does not receive the SMS message.

Common and Known Issues Related to SMS Delivery

Some carriers block SMS messages from international networks by default.

If you are sending SMS messages to a cellphone, you should first try reaching out to your local carrier and confirm that the cellphone can receive SMS messages from +882 phone numbers. If you do not use the Hologram REST API, Python SDK, or CLI, the outbox number for SMS messages will always be from a +882 number. This is true even if you purchased a phone number.

If your local carrier cannot support delivery of SMS messages sent from +882 numbers, try purchasing a phone number with your country code and send SMS messages using the Hologram REST API, Python SDK, or CLI.

SMS on Cat-M1 is not yet fully supported by all networks.

This is usually due to timing issues related to the longer sleep duration on newer power efficient networks like Cat-M1. We expect these to improve with time, but it is hard to give a timeline given that these are network maturity issues that each carrier addresses as they see fit. 

We have also observed that for some Cat-M1 networks, both the sending and receiving devices must be connected to the same Cat-M1 network for the SMS messages to be delivered.

Cat-M1 is an IoT-specific radio access technology designed for the Internet of Things. Carriers' focus is on improving the packet-switched (data/Internet) issues on the network before focusing on the circuit-switched (SMS) issues.

Networks have incorrectly mapped and configured Short Message Service Center (SMSC) routing.

SMS delivery relies on the assumption that every network has correctly mapped and configured  the Short Message Service Center (SMSC) routing. This assumption is not always true. If the mapping and configuration is incorrect for one of the networks involved, then SMS messages will not always reach their destination. Both the network your Hologram device is connected to and the network of the receiving device must be mapped and configured properly. Individual carriers manage their mapping, so Hologram cannot update these configurations.

Additional Troubleshooting Steps

  1. Check the Hologram status page to confirm there are no open issues affecting the REST API or SMS.
  2. Confirm both the sending and receiving devices are powered on and have adequate signal.
  3. Confirm the receiving device can receive SMS messages from non-Hologram devices.
  4. Test with different device on the same carrier as the receiving device. Confirm that the second device can receive Hologram SMS messages.


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