The short answer: if your missed call text back shows as "sent" but customers say they never got it, the first thing to check is whether the number sending the text is registered for A2P 10DLC. In the US, carriers block business texts sent by software from unregistered 10-digit numbers, and the failure is often invisible on your end.
Work through the checks below in order. Each one is quick.
1. Is the sending number registered?
Twilio's documentation says anyone sending SMS or MMS over a 10DLC number from an application to the US must register for A2P 10DLC, and that carriers block A2P traffic to US recipients from unregistered Twilio 10DLC numbers. Its changelog says that blocking took effect September 1, 2023, and that Twilio's error code for it is 30034, "US A2P 10DLC: Message from an Unregistered Number." Twilio also says messaging rates still apply to blocked messages, so you can pay for texts that never arrive.
What to do: ask your text-back vendor, or check the console if you use a provider directly, whether your number is tied to an approved brand and campaign. If it is not, registration is the fix. Our post on A2P 10DLC registration for contractors walks through it.
Other vendors and carriers report different enforcement dates, so treat the Twilio date as applying to Twilio numbers only. If you use another provider, check its own documentation.
2. Is the registration approved, or still pending or rejected?
Twilio's error documentation lists an unfinished brand or campaign registration as a cause of error 30034. A campaign that was submitted but not approved does not clear your number to send.
Campaign rejections often involve the opt-in description. Twilio's rejection codes cover things like an incomplete description of how customers consent, a missing privacy policy or terms link, pre-checked consent boxes, and opt-in evidence that shows a different company name than the registered brand. If your campaign was rejected, read the reason code, fix that one item and resubmit.
3. Is the number attached to the approved campaign?
Registration is not enough on its own. Twilio's error documentation says the number must be in the sender pool of the messaging service linked to the approved campaign. A number bought after registration is easy to forget. Add it, and confirm its status.
A related limit: Twilio says only one 10DLC number can be registered to a sole proprietor campaign, so extra numbers on that campaign remain unregistered.
4. Did a carrier or Twilio filter the message?
A registered sender can still have a message filtered. Twilio's error 30007 means the message was filtered by Twilio or by the carrier. CTIA's Messaging Principles and Best Practices (May 2023) say service providers may filter or block unwanted messages. Content that looks like spam, such as a bare link, heavy capitalization or a message that does not name your business, is more likely to be flagged. Keep the wording plain and identify your company.
5. Is it a toll-free number?
Toll-free numbers have their own verification requirement. Twilio's toll-free documentation says an unverified or rejected toll-free number cannot be used to send messages, and that Twilio reviews requests within three business days. If your text-back runs on a toll-free number, check its verification status.
6. Did the customer opt out earlier?
CTIA's guidance says that once someone texts STOP, the sender sends one confirmation and then stops. If a customer replied STOP to an earlier text, later messages to that number will not go through, and that includes your automatic text-back.
7. Is the trigger firing at all?
If none of the above applies, the problem may be upstream. Confirm that your phone system actually raises a "missed call" event. Common gaps are calls forwarded from a main line that the system sees as answered, calls that ring to a mobile phone and go to carrier voicemail, and business hours settings that suppress the text. These are general troubleshooting steps rather than findings from a specific vendor, so check your own system's settings.
8. Test it like a customer
Call your own business number from a phone that is not in your contacts, let it ring out, and see whether the text arrives and how long it takes. Do this on a Friday evening as well as a weekday morning, and from phones on different carriers. A text that works for one carrier and fails on another points to filtering.
When it keeps failing
If you have gone through the list and the text still does not arrive, send the provider's support team the failed message IDs and error codes. Twilio asks for at least three message SIDs with an undelivered status and error 30007 for filtering disputes.
To size what unreceived texts may be costing you, see what a missed call really costs a contractor. For the full setup, including wording and reply routing, see missed call text back for contractors. If you text customers, also read TCPA texting rules for contractors, which is general information and not legal advice. If you want the registration, text-back and follow-up handled together, that is part of our AI lead generation and follow-up work.