Use this glossary to identify what went wrong when a message fails to deliver in Sense Messaging — and what to do about it.
Mobile carriers return a wide range of delivery codes (DLR codes) when a message can't be delivered. Sense translates these into the error codes below so you can diagnose issues and take action without having to decode raw carrier data.
Before contacting Sense Support for any error listed below, include the following in your support request:
- Your Sense number
- The candidate's number(s)
- The error code(s) you received
This helps the team investigate faster and avoids delays from reviewing screenshots.
Recipient & Device Errors (1xxx)
1001 — SMS Error: Recipient Device Offline
The carrier tried to deliver your message but couldn't reach the recipient's phone. This is the most common error in Sense Messaging. Carriers will occasionally use this code when filtering messages, but in most cases the device is simply unreachable.
Common reasons
- The recipient's phone is switched off, roaming, out of the country, or has no signal
- The device cannot receive SMS (for example, the number belongs to a landline)
- The mobile number is no longer active — common with burner phones
- On T-Mobile, this can sometimes relate to 10DLC provisioning
- In some cases, the recipient has blocked SMS from your sending number
What to do
- Wait a few hours or a day or two and retry the message
- Try calling the recipient — if you hear a disconnect or "cannot be reached" message, that explains the failure
- Retry from a different sending number in your account
When to contact Support
Call the recipient first to confirm the line is active. If you're confident they should be reachable and messages are still failing, contact Sense Support with:
- From Number
- To Number
- Date of the message(s)
Resolution timeline
In most cases, this error resolves on its own once the device comes back online. 10DLC provisioning issues are generally resolved within 1 business day. Carrier filtering issues typically resolve in 2–3 business days.
1002 — SMS Error: Recipient Device is Landline
The number you're messaging belongs to a landline and cannot receive texts. Don't retry — this number will never receive SMS.
Common reasons
- The recipient's phone number is a landline or otherwise cannot receive SMS
What to do
- Update your ATS data to stop further contact attempts to this number
When to contact Support
In rare cases, a landline number can become a mobile number. This data is managed through the North American Numbering Plan (Neustar) and updated quarterly — not in real time. If you believe this applies, contact Sense Support with:
- From Number
- To Number
- Date of the message(s)
Resolution timeline
This error is almost always permanent. In the rare case of a landline-to-mobile conversion, resolution can take several weeks.
1003 — SMS Error: Recipient Blocked Sender
The recipient has blocked your number on their device. Messages cannot reach them until they unblock you.
Common reasons
- The recipient has blocked your sending number
- The recipient has blocked all unknown senders
What to do
- If you believe the block was unintentional, use an alternative method to contact the recipient and ask them to unblock your number
When to contact Support
This is rarely a system issue. You can reach out to Sense Support if you'd like, but the standard resolution requires the recipient to contact their wireless carrier. Include:
- From Number
- To Number(s)
- Date of the message(s)
Resolution timeline
Sense Support cannot resolve this error in most cases.
1004 — WhatsApp Error: Recipient Not on WhatsApp
The number you're messaging isn't registered with WhatsApp. The message cannot be delivered.
Common reasons
- The recipient doesn't have WhatsApp tied to their phone number
What to do
- If you're in a supported country, try SMS as a backup channel
When to contact Support
Sense Support cannot resolve this error.
Resolution timeline
N/A
Volume & Compliance Errors (2xxx)
2001 — SMS Error: 10DLC Volume Violation
Your account has exceeded its carrier-assigned sending limit — either messages per second, or T-Mobile's daily segment cap.
Common reasons
- Your sending volume exceeds the throughput allowed by your Campaign Registry 10DLC Brand Score
- You've hit T-Mobile's daily message cap for your Brand Score
What to do
- Spread broadcast messages over a longer time window
- Work on increasing your 10DLC Brand Score
When to contact Support
Contact Sense Support — in some cases, we can help improve your brand score to increase volume limits across carriers and raise T-Mobile message limits.
Resolution timeline
Contact Sense Support for details. Resolution timelines vary based on your specific circumstances.
2002 — SMS Error: 10DLC Campaign Issue
There's a compliance issue with your account's 10DLC messaging registration that's blocking delivery. Contact support immediately — this can impact your ability to send messages until it's resolved.
Common reasons
- Your sending number has fallen out of 10DLC provisioning and is non-compliant
- There's an issue with your 10DLC Campaign registration
What to do
- Contact Support right away
When to contact Support
Contact Sense Support as soon as possible. Include:
- To Number(s)
- From Number
- Date of the message(s)
Resolution timeline
This can take time to resolve and may result in a significant delay to your sending. Don't wait — contact support immediately.
Content Errors (3xxx)
3001 — SMS Error: Message is Too Large
Your message is too long for the carrier to deliver. Shorten it or remove emojis and retry.
Common reasons
- Your message exceeds the carrier or connection partner's segment limit
- Excessive emoji use inflates message size by increasing the number of segments required
- The message is simply too long
AT&T generally supports up to 11 segments per message. Verizon and T-Mobile support slightly more.
What to do
- Shorten your message — SMS is designed for brief content
- Remove all emojis and resend
When to contact Support
You can resolve this one without contacting Support.
Resolution timeline
Immediate, once you've shortened the message or removed emojis.
3002 — SMS Error: Message Rejected as Spam
The carrier flagged your message as potential spam and blocked it before it reached the recipient.
Common reasons
- Review your message for spammy words to avoid, redraft, and resend
- Too many special characters — particularly $ and !
- The carrier's complaint feedback loop has received a high volume of spam reports from your sending number
- Your embedded link was blocked — this happens frequently with commercial link shorteners like bit.ly or tinyurl.com
- Too many emojis in the message
- The @ symbol was used for something other than an email address
- Too many words written in ALL CAPS
What to do
- Redraft your message, avoiding known spam trigger words, and resend
- Use corporate-branded links instead of commercial link shorteners
- Limit special characters — no more than one $ and one ! per message
- Use "at" for locations, reserve @ for email addresses only
- Cut back on emojis
- Avoid excessive capitalization
When to contact Support
If one or two messages to the same recipient get marked as spam but others go through, you likely hit a content filter — adjust your message and URL following the guidance above, and resend. Don't contact support for isolated cases.
If you're seeing this error at a higher frequency than usual, contact Sense Support. Include:
- From Number
- To Number(s)
- Date of the message(s)
Resolution timeline
Most spam remediations resolve within 2–4 business days. In extreme cases, AT&T has implemented 30-day lockdowns.
Delivery & Timing Errors (4xxx)
4001 — WhatsApp Error: WhatsApp Frequency Cap Reached
The recipient has already received the maximum number of marketing messages from businesses via WhatsApp in the last 24 hours — not just from you. Try again the following morning.
Common reasons
- Too many marketing template messages have been sent to this recipient within a 24-hour window across all businesses. For example: if two other businesses sent marketing templates to a contact at 9 AM and 10 AM, and you try at 11 AM, Meta may block your message for the remainder of that 24-hour period. This is Meta's spam prevention at work.
What to do
- Retry the message first thing the next morning
When to contact Support
Support cannot resolve this issue.
Resolution timeline
N/A
4002 — SMS Error: Message Sent but Delivery Unknown
Your message was most likely delivered, but the carrier couldn't confirm it. No action is usually needed.
Common reasons
- Network congestion caused the carrier to time out the delivery receipt, or the handset never returned one
What to do
- If you're confident the message wasn't received, retry at a later time
When to contact Support
If you receive this error for more than 30 messages sent in a short period, contact Sense Support. Include:
- From Number
- To Number(s)
- Date of the message(s)
Resolution timeline
This is common during high-traffic periods like Thanksgiving week. It typically resolves on its own within 1–6 hours as network latency clears.
4003 — WhatsApp Error: WhatsApp Session Window Expired
The 24-hour conversation window for free-form messages with this recipient has expired. Send a new template message to reopen it.
Common reasons
- A free-form (non-template) message was sent after the 24-hour conversation window closed
What to do
- Send a new templated message to the candidate to reopen a fresh 24-hour window
When to contact Support
Support cannot resolve this issue.
Resolution timeline
N/A
4004 — SMS & WhatsApp Error: Provider Rate-Limited
Messages are failing because your account is sending faster than the carrier allows. Contact support immediately.
Common reasons
- Network congestion
- Your send rate exceeds the carrier's accepted throughput
What to do
- Contact Support immediately
When to contact Support
Contact Sense Support as soon as possible.
Resolution timeline
This typically resolves within 1–6 hours.
Sense Platform Errors (5xxx)
5001 — Sense Error: Recipient Opted-Out
The recipient has opted out of text messages from your agency and subscription category. Do not message this contact again.
Common reasons
- The candidate replied STOP to one of your messages
- The candidate opted out via another system, and your ATS synced that opt-out to Sense
What to do
Nothing — this contact should not be messaged again.
When to contact Support
Support cannot resolve this issue.
Resolution timeline
N/A
5006 — Sense Error: Outside Broadcast Window
This message was sent outside your organization's allowed broadcast hours. Retry during the configured window.
Common reasons
- A broadcast was triggered or scheduled outside your organization's allowed sending window
What to do
- Retry the broadcast at a time within your allowed window
When to contact Support
Support cannot resolve this issue. Contact your Sense Administrator to confirm your organization's broadcast window settings.
Resolution timeline
N/A
5007 — Sense Error: Segment Limit Exceeded
Your message exceeds Sense's internal segment limits. Shorten your message or remove emojis and retry.
Common reasons
- The message is too long
- The message contains too many emojis
For more on how segments work, see Introducing Segments in Messaging.
What to do
- Shorten your message and resend
- Remove emojis from your message
When to contact Support
Segment limits can be raised on a case-by-case basis. Contact Sense Support and they'll connect you with your assigned Account Executive.
Resolution timeline
N/A
Unknown Errors (9xxx)
9001 — SMS & WhatsApp Error: Unknown Failure
Something went wrong that doesn't match any standard error category. Our team is automatically notified — contact support with your details so we can investigate.
When to contact Support
Contact Sense Support and include:
- From Number
- To Number(s)
- Date of the message(s)
Resolution timeline
Dependent on the specific issue.