There it is in RingCentral app gallary: https://www.ringcentral.com/apps/redtail-crm

Also here: https://ringcentral.github.io/redtail-embeddable-ringcentral-phone/

This is maybe one of the worst "apps" I have every seen. It simply does not work. They clearly did not work with Redtail to develop a proper integration. This is a security nightmare if you read the code. Ringcentral just go to Redtail and develop something.

It's an app from a community (Published by RingCentral Labs). It's not an official integration. You just asked for an integration and when someone helped you with that. If this does not work for you, then the answer is no RedTail CRM integration.