All Delivery Receipts with a non-zero error code can be considered as indicating failed delivery. i.e. Your SMS did not reach the recipient.
Neither Nexmo SMS APIs nor operators will perform further attempts to re-deliver a message unless another API call is performed.
Nexmo error codes:
err-code field in the DLR provides more detailed information and can help troubleshoot a failed delivery. A non-zero code indicates that the message could not be delivered.
|0||Delivered||Message was delivered successfully|
|1||Unknown||Message was not delivered, and no reason could be determined|
|2||Absent Subscriber - Temporary||Message was not delivered because handset was temporarily unavailable - retry|
|3||Absent Subscriber - Permanent||The number is no longer active and should be removed from your database|
|4||Call Barred by User||This is a permanent error:the number should be removed from your database and the user must contact their network operator to remove the bar|
|5||Portability Error||There is an issue relating to portability of the number and you should contact the network operator to resolve it|
|6||Anti-Spam Rejection||The message has been blocked by a carrier's anti-spam filter|
|7||Handset Busy||The handset was not available at the time the message was sent - retry|
|8||Network Error||The message failed due to a network error - retry|
|9||Illegal Number||The user has specifically requested not to receive messages from a specific service|
|10||Illegal Message||There is an error in a message parameter, e.g. wrong encoding flag|
|11||Unroutable||Vonage cannot find a suitable route to deliver the message - contact email@example.com|
|12||Destination Unreachable||A route to the number cannot be found - confirm the recipient's number|
|13||Subscriber Age Restriction||The target cannot receive your message due to their age|
|14||Number Blocked by Carrier||The recipient should ask their carrier to enable SMS on their plan|
|15||Prepaid Insufficient Funds||The recipient is on a prepaid plan and does not have enough credit to receive your message|
|50||Entity Filter||The message failed due to
|51||Header Filter||The message failed because the header ID (
|52||Content Filter||The message failed due to
|53||Consent Filter||The message failed due to consent not being authorized. More information on country specific regulations|
|54||Regulation Error||Unexpected regulation error - contact firstname.lastname@example.org|
|99||General Error||Typically refers to an error in the route - contact email@example.com|
For further information see: Why was my SMS not delivered?