These are the mose 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

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

*There is an issue with the mobile carrier
*Can the device receive non-Twilio SMS/

*Can the devce receive messages from another Twilio number (non-Alpanumeric Sender ID), or with a shorter one-segment (non-concatenated) body?
30006
Landline or Unreachable Carrier 
*Your message was sent to a landline, or an unreachable carrier for the phone number type.
*Use the lookup APi to determine if the number is indeed a landline. If it is not, try with an alternative phone number type.
30007
Message Filtered 
*Your message was identified as spam or unwanted messaging by Twilio's message filtering system

*Your message was flagged as objectionable and blocked by a wireless carrier 
*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.