Too many messages have been sent between two numbers within a short time period, possibly indicating a runaway job or infinite loop. There is a limit of 20 outbound replies between two phone numbers in a short period.
A counter is set for each outbound TwiML reply in a conversation (between two numbers). When the first reply occurs, the counter starts at 1. If the next reply is sent less than 15 seconds after the prior reply, then the counter goes to 2. This will continue if each reply is less than 15 seconds, until the counter surpasses 20; at this time, Twilio will set any further messages in the loop to "failed" status for 30 seconds, with this error code. Messages with the "failed" status are not charged against your account balance.
- repeated rapid responses by the end user (less than 15 seconds)
- infinite loop caused by self referencing Sms or Message verb action URL
- infinite loop caused by self referencing Redirect verb URL
- runaway process making repeated outgoing REST API requests
- make certain any action or Redirect URL's do not loop back to the same TwiML document.
- make sure you are not inadvertently sending a large quantity of messages to the same phone number, e.g. a script caught in a loop