The calling party number to use when placing the call to the dialed number

number to dial and start call sessions with.

URL for sending notifications after call gets completed or failed

A user-provided arbitrary string value that will be stored with the call status and sent in all callback events.

An optional user provided value that is used to prevent duplicate requests. API requests with an Idempotency-Key value that has been used in the previous 1 hours will be rejected as a duplicate request.