These are the more popular codes that have been seen. Here is a link to the view the other code https://www.twilio.com/docs/api/errors#3-anchor


ERROR CODE
ERROR DESCRIPTION
POSSIBLE CAUSES
POSSIBLE SOLUTIONS
30002   Account Suspended 
 
Your account was suspended between the time of message send and delivery. Please contact Twilio. This message failed because your account was suspended after this message was queued but before it was sent by Twilio 

*Account was suspended for lack of funds after your message was queued but before it was sent ny twilio

*Account was suspended because Twlio detected a violation of their Acceptable Use Policy




30003 Unreachable Destination Handset
The destination handset you are trying to reach is switched off or otherwise unavailable *The destination handset you are trying to reach is switched off or otherwise unavailable

*The device you are trying to reach does not have sufficient signal

*There is an issue with the mobile carrier 
 The first step to troubleshooting this issue is to attempt to replicate the problems. Attempt to send another test message to this user first. 
  *Can the device receive non-Twilio SMS/

*Can the device receive messages from another Twilio number (non-Alphanumeric Sender ID), or with a shorter one-segment (non-concatenated) body? 
If the problem persists, try verifying if the number you are sending out SMS to is NOT a landline. Use this website:https://www.phonevalidator.com/
30006   Landline or Unreachable Carrier
SMS being sent to Landline or Short Code
*The destination number is unable to receive this message. Potential reasons could include trying to reach a landline or, in the case of short codes, an unreachable carrier
*Make sure that the number you are sending out SMS to is not a Landline or Short Code number
30007   Message Filtered 
Message Filtered 
* Your message was filtered (blocked) by Twilio or by the carrier

* Twilio's filtering system is in place to protect mobile subscribers from spam or other forms of malicious or unwanted messages


*Wireless carriers have filtering systems in place as well. The carrier filters are used to block abusive traffic, as well as enforce rules or regulations about what type of messaging are allowed to that country or mobile network. 
*Ensure your messaging use case complies with Twilio's Messaging Policy and Acceptable Use Policy 


*Review the information in How Does Message Filtering Work? to understand what causes filtering.

*See How do I prevent my Twilio messages from being filtered (blocked)? for specific tips on avoiding message filtering.