When sending messages through Udext, you may occasionally see error codes on certain contacts or messages. These codes are returned by mobile carriers and messaging providers and indicate why a message could not be delivered.
This article explains:
What each error code means
Why you’re seeing it
What (if anything) you can do to fix it
Important: Many delivery errors are determined by the recipient’s device or mobile carrier and are outside of Udext’s control.
Common Error Codes and How to Resolve Them
30008 — Unknown Carrier Delivery Failure
What it means
The mobile carrier failed to deliver the message but did not provide a specific reason.
Why this happens
Temporary carrier or network issues
Delivery routing failures
The carrier could not confirm delivery to the device
What you can do
Retry sending the message later
Confirm the phone number is valid and active
If this happens repeatedly across many contacts, reach out to Udext support
30003 — Unreachable destination handset
What it means
The recipient’s device could not be reached at the time of delivery.
Why this happens
Phone is powered off
No cellular signal or network coverage
Device temporarily unavailable
What you can do
No action is required
Messages may deliver automatically once the device reconnects
Retry later if needed
30004 — Message Blocked
What it means
The message was blocked before reaching the recipient.
Why this happens
The recipient blocked messages from your sender
Carrier-level blocking
Device-level messaging restrictions
Prior opt-out behavior
What you can do
Confirm with the contact that messages are not blocked
Ask the contact to adjust their device or carrier settings
Avoid retrying repeatedly, as the message will continue to fail
30005 — Invalid or Inactive Phone Number
What it means
The phone number is not valid or is no longer in service.
Why this happens
Number has been disconnected or deactivated
Number does not exist
Incorrect or outdated contact data
What you can do
Verify the phone number with the contact
Update or remove the invalid number from your contact list
30006 — Landline or unreachable carrier
What it means
The phone number cannot receive SMS or MMS messages.
Why this happens
Landline number
Voice-only or unsupported number type
Carrier does not allow messaging to this number
What you can do
Replace the number with a mobile number that supports SMS
Exclude this contact from future SMS messages
30007 — Message filtered
What it means
The message was blocked by carrier filtering or compliance rules.
Why this happens
Message content triggered carrier spam or compliance filters
Regulatory or policy restrictions
High-risk message patterns
What you can do
Review message content and tone
Avoid spam-like formatting or wording
If this affects many contacts, contact Udext support
21610 — Contact Opted Out
What it means
The recipient has unsubscribed from receiving messages.
Why this happens
Contact replied with an opt-out keyword (e.g., STOP)
Consent was revoked
What you can do
Do not send messages to this contact
Messaging can only resume if the contact explicitly opts back in by replying back with START
21211 — Invalid Phone Number Format
What it means
The phone number is incorrectly formatted.
Why this happens
Missing country code
Extra characters or spaces
Incorrect digit length
What you can do
Update the number to international (E.164) format
Example:+15551234567Correct and re-import the contact
21408 — Messaging Restricted by Region
What it means
Messages to this geographic region are currently restricted.
Why this happens
Regional regulations
Carrier or country-level restrictions
What you can do
Confirm messaging is supported for the destination region
Contact Udext support if this impacts a critical workflow
Things to Keep in Mind
Some errors are temporary and may resolve automatically
Others are permanent and require updating or removing the contact
Carrier decisions are outside of Udext’s control
If you’re unsure how to handle a specific error or are seeing repeated failures, our support team is happy to help.
Questions? Chat with us or email [email protected]