If an SMS is undeliverable or an outbound call is not able to be made, the system may notify you with a 5 digit error code, such as 30003 or 21610. Twilio provides a thorough list of error codes, but it’s important to know the ‘gatekeeper’ making the determination of message deliverability is the recipient/destination phone carrier (i.e. if you’re sending to Verizon, ATT, etc.). The phone carrier determines if a message is spam/phishing, if the number is a landline, or if there is another reason the message cannot be delivered.
Having a specific error code allows you to troubleshoot the specific reason the SMS or call failed. Twiilio has a full library of error codes that offers an explanation of each error, along with possible causes and solutions. Check out this link for details on each error code: https://www.twilio.com/docs/api/errors
You can review a particular error, and then determine the appropriate course of action to resolve the issue.
There are a few different places you may find Twilio error codes within the system. Within an individual contact record, in the center column where you can view communication history. A failed outbound call or SMS will have a red triangle icon, as shown below. You can click on that to open the error code message which gives you the code number: 30008 (explained in depth in Part 3 below.)
You may also click into a campaign, and click “show detail” to view success/failures of a specific campaign event. In the pop-up window, under the Failed tab, the error code 30008 appears:
Below is a list of commonly seen Twilio errors. Check out the list below for some of the most common errors you may experience, and be sure to check out Twilio’s error message library for a more extensive list of every error code, possible causes, and potential solutions.
Error 21610: the destination/recipient number has opted out of messages. They’ve unsubscribed or replied STOP, and they will need to reply START in order to resolve this issue.
Error 30003: unreachable destination handset. This means the destination/recipient is currently unable to receive messages (unlike 30006 which indicates a permanent situation like a landline, 30003 is more often temporary.) Perhaps the phone is powered off, on airplane mode, or out of signal range.
Error 30005: unknown destination handset. This means the number could be off/out of range, it could be a landline, or it could be a number not in service.
Error 30006: the destination/recipient number is unreachable (most likely as a landline).
Error 30007: message filtered. Phone carriers may flag and filter messages that appear to be spam, phishing, or fraud. This message could be filtered due to violating Twilio’s Messaging Policy or Acceptable Use Policy, or could be filtered by the carrier due to their specific rules.
Error 30008: generic error. When a carrier partner notifies Twilio of a generic error to deliver a message without detailed explanation, Twilio will return a 30008 code.
