In SMS.to Reports, you can easily track the status of your sent messages. The report will show you not only the messages that have been successfully delivered but also those that failed to reach the recipient. 



Understanding why these messages did not reach the end recepient is crucial for optimizing your SMS delivery issues. 

If the message has failed, you will be able to see the reason for the failure under the 'Status' column. For example:



Below, we’ve provided an overview of the common error codes you may encounter when a message fails, along with explanations for each:



Error CodeError ReasonExplanation
1
Unknown SubscriberThe “Unknown Subscriber” error typically originates from the Home Location Register (HLR) or the Home Subscriber Server (HSS) in GSM/LTE networks.
The HLR/HSS is responsible for storing subscriber information (IMSI, MSISDN, services, roaming data, etc.).
When an SMSC (Short Message Service Center) or signaling entity queries the HLR for routing information to deliver an SMS, the HLR returns Unknown Subscriber when: 
  • The MSISDN does not exist in its database, 
  • The MSISDN used to exist but was deleted, deactivated, or ported incorrectly, or 
  • There's no valid mapping between the MSISDN and IMSI (the SIM identity).
2Unknown Base StationAn unidentified or unrecognized base station, often in the context of network or communication systems. This could be due to a missing or inaccessible base station.
3Equipment protocol ErrorEquipment protocol error.
4Equipment not equipped for SMEquipment not equipped with short-message (SMS) capability.
5Unidentified Subscriber

The destination number doesn’t exist or can’t be found in the network’s subscriber database.

It’s a permanent, non-recoverable delivery error, usually requiring the sender or operator to validate or remove the MSISDN from active campaigns.
6

Illegal Subscriber

The mobile station (handset) failed authentication
7

Teleservice Not Provisioned

Teleservice not provisioned. Mobile subscription identified by the MSISDN number does not include the short message service.
8

Illegal Equipment

IMEI Check failed, IMEI is either blacklisted or not Whitelisted
9

Handset Memory Full

Handset memory capacity exceeded. Handset has run out of free memory to store new message.
The only solution for that is to delete old and unneeded messages from your SMS inbox
10Unknown EquipmentThe mobile device has not been recognized by EIR (Equipment Identity Register) during device verification on the MAP protocol level at the operator’s infrastructure.
13Mobile Handset Switched OffThe mobile device is turned off or was turned off at the moment that the message was sent
16Absent SubscriberAbsent subscriber. No paging response via MSC.
17Absent SubscriberAbsent subscriber. IMSI detached.
18Absent SubscriberAbsent subscriber. Roaming restriction.
21Facility Not SupportedNot supported by the handset or the network being used due to limitations, restrictions, or incompatibility.
Resolving this error typically involves:
  • Verifying the supported facilities or services 
  • Ensuring the subscriber's compatibility with the requested feature
  • Handset devices restart
  • Applying the newest software/firmware updates.
27Absent SubscriberThe destination numbers provided during the submissions were unreachable:
  • Not properly connected to the operator's network or,
  • Powered off or,
  • Located in an area with limited/low coverage or 
  • Subject to roaming restrictions.
Resolving this error involves ensuring that the subscriber's device is turned on and has a stable network connection.
30Subscriber Busy For MT SMSSubscriber Busy For MT SMS
31SMS ExpiredSMS has expired after attempting delivery for too long
34System FailureSystem Failure
35Data MissingData Missing
36Unexpected Data ValueUnexpected Data Value
37SenderID not RegisteredSenderID is not Registered to that Network/Country, please contact support at : support@sms.to
38Number not registered in networkUnknown subscriber: The number is not allocated.
An Unallocated number is a valid phone number that does not belong to any subscription. 
There are two clear reasons for this. 
  1. The number is not assigned to a service provider. 
  2. But the administrator or the service provider has already transferred it, but no subscriber has allocated it yet.
Then, if someone dials this specific number, the caller cannot connect to a subscriber. Instead, the caller would hear this automatic message.
2001Blacklisted Destination Number
The destination number has been blacklisted either at the operator`s request or on your account via the SMS.to web interface.
2002Blacklisted Sender Address
The sender number has been blacklisted either at the operator's request or on your account via the SMS.to web interface.
3000Unknown ErrorError not yet mapped or not shared by provider/operator