The Client Insights beta ended in August 2019 with the general availability of Voice Insights. We have continued to respond to requests made to the preview API, but we will cease responding to requests to beta API resources on May 1, 2020.
If your application consumes the preview API resources you will need to update your code to use the new endpoints. We have created a migration guide to assist with update your applications: https://www.twilio.com/docs/voice/insights/client-insights-preview-api-shutdown/client-insights-preview-api-migration-guide
For more information about the shutdown of the Client Insights preview API see https://www.twilio.com/docs/voice/insights/client-insights-preview-api-shutdown