Understanding timeouts and retries
The PSTN Audio service interacts with AWS Lambda functions synchronously. Applications
wait 5 seconds for AWS Lambda functions to respond before retrying an invocation. When a
function returns an error with one of the 4XX status codes, then
by default the SIP media application only retries the invocation once. If you run
out of retries, calls terminate with the 480 Unavailable
error code.
For more information about AWS Lambda errors, see Troubleshoot invocation
issues in AWS Lambda.