For Basic and Standard Notification Hubs tiers, properly configured applications can send push notifications or perform registration management operations at least 99.9 percent of the time. To learn more about the SLA, go to the Notification Hubs SLA page.
Note
Because push notifications depend on third-party Platform Notification Systems such as Apple's Push Notification Service (APNs) and Google's Firebase Cloud Messaging (FCM), there is no SLA guarantee for the delivery of these messages. After Notification Hubs sends the batches to Platform Notification Systems (SLA guaranteed), it is the responsibility of the Platform Notification Systems to deliver the pushes (no SLA guaranteed).