Product: Programmable SMS
Twilio queues messages based on the sending rate of a sender or an account. For example a US long code number can send one message segment per second.
Messages can only be queued for 4 hours and then they automatically fail. You can monitor the length on your queue via the Queue Insights dashboard.
For more information please view this FAQ.
- You tried to send too many messages too quickly and your message queue overflowed.