Why are my messages ‘undelivered’?

Occasionally messages from Twilio will not reach the end user and will be marked with a status of “undelivered”.  There are multiple reasons for why the message may not have been received. A list of these reasons can be found based on the ‘Error Code’ provided.

Note, in some cases the status may remain ‘sent’ although the message was not actually delivered to the phone. This may be because Twilio did not receive a status update from the network handling delivery.