pushtotalk is not a valid value for apns-push-type in Firebase cloud messaging

Hello, we are unable to use the ios push to talk framework using cloud messaging. it says that Error: Invalid [apns-push-type] set for apns platform. IOS manual says that the push type to be set to pushtotalk. but thsi s not allowed in messaging().send(message) const message = { notification: { title: 'test' }, apns: { headers: { 'apns-push-type': 'pushtotalk', 'apns-topic': ***.***.***.voip-ptt', 'apns-priority' : '10', 'apns-expiration' : '0' }, payload: { aps: { 'mutable-content': 1 } }, fcm_options: { } }, webpush: { headers: { } }, topic: topicval