A reply request should have an object as parameter, and the
object should have a member call_id that specifies the
identifier of the active call to retry, i.e. the call to
backtrack into to obtain a new solution from the call hook.
Please note: Currently, only the most recent active call
can be the target of a reply request.
When the active call is retried the result from the call hook will be handled in the same way as the initial call. I.e. if the call hook succeeds again, the call is still active (with the original call id), if the call fails or throws an error, the call is closed.