Thank you for your response. I have an additional question. You mentioned that to update the device token, it is recommended to launch the app and execute didRegisterForRemoteNotificationsWithDeviceToken. However, is it possible to update the device token in the background without launching the app? If it is possible, I would appreciate it if you could explain how to update the device token in the background without launching the app.

Number and frequency of notification splits.

Notifications are not split into 1000 items each time. The number of cases changes every time, sometimes reaching 1,500 or 2,000 cases, so I don't think it's a problem with the HTTP channel. Also, even if you send the same number of items, the number of times they will be divided will be different each time. The notification was sent to APNS from MSAzure's NotificationHubs, and we asked MSAzure to investigate. We have confirmed that several thousand items can be sent from NotificationHubs to APNS at once. However, due to a delay on the APNS side, there was no response returned to NotificationHubs, and the response was that it was waiting. Is there anything we can learn from this?