The specified validity period on this message has elapsed.
The message has spent more than the specified amount of time in Twilio's system. This can be due to a long time spent in the queue due to a combination of your messaging rate limits, the number of messages submitted in rapid succession, and the amount of time you have allotted via the ValidityPeriod setting in your messaging service or on the message itself.
You can retry the message with a longer validity period and avoid sending very large batches of messages at a rate that far exceeds your messaging rate limits.