When I make a phone call using RingOut API, the Webhook sends out events with 2 different telephonySessionId. I know that this is a two-legged call, which will produce a telephonySessionId for each leg. But all the events sent out by a single call should have a consistent ID to help the client aware of the full flow and can decide which event to handle, and which one to ignore.
My suggestion is having an attribute named originalTelephonySessionID in all events related to a RingOut call, its value should be exactly the same as the ID returned from the RingOut API response.

Having a new attribute like this will not break any existing integrations, but will help others a lot in the advanced Webhook integration.
Thank you!