Callee Answered event not being sent to webhook

We have been using webhooks for Zoom Phone and we are receiving events when outbound calls are started but not when inbound calls are answered. Both caller and callee events are selected in the webhook configuration (especially callee_answered, callee_missed and callee_ringing events) But none of these trigger the event to our webhook. We are responding with 200 ok to all events received and have no problem with any other events.