Welcome to the RingCentral Community

I found the references and clues here in this link - http://ringcentral-api-docs.readthedocs.io/en/latest/webhooks/

Please read the requirements of RingCentral WebHooks: https://medium.com/ringcentral-developers/common-questions-on-webhooks-8dd3550f4525

1. is available on the Internet because the URL needs to be public and accessible.
2. Uses TLS 1.1 or greater / has SSL enabled (ie: https://, only need this in production). For Development TLS is not necessary.
3. responds within 3000 milliseconds
4. responds with Validation-Token header on subscription request (mentioned later in article)
5. should NOT respond with a body larger than 1024 bytes — if the body is too large you will get {“errorCode”:”SUB-525",”message”:”WebHook server response is invalid”} when setting up the WebHook

TLS / SSL only needs to be enabled in production. For development purposes, TLS is not necessary.

For development purposes, you can use localhost along with a service like ngrok.