PushNotification not working

Hi, I have a problem with push notification on iOS, the notification is displayed when the app is runnning but, when it is in background, nothing happen. Server side I have this error:

Push ➔ debug Could not send notification id: “undefined”, Error: Cannot read property ‘send’ of undefined
Push ➔ debug TypeError: Cannot read property ‘send’ of undefined
at sendAPN (app/push/server/apn.js:48:16) at PushClass.sendNotificationNative (app/push/server/push.js:87:5)
at app/push/server/push.js:208:16
at SynchronousCursor.forEach (packages/mongo/mongo_driver.js:1138:16)
at Cursor. [as forEach] (packages/mongo/mongo_driver.js:918:44)
at PushClass.sendNotification (app/push/server/push.js:201:35)
at PushClass.send (app/push/server/push.js:325:9)
at PushNotification.send (app/push-notifications/server/lib/PushNotification.js:70:15)
at NotificationClass.push (app/notification-queue/server/NotificationQueue.ts:95:20)
at app/notification-queue/server/NotificationQueue.ts:67:12
at /opt/Rocket.Chat/programs/server/npm/node_modules/meteor/promise/node_modules/meteor-promise/fiber_pool.js:43:40