I'm developing an iOS application. The backend/server needs to send push notifications to the iOS application. What is the best and most reliable way of doing so? I need the application to receive notifications even when not running or in the background or terminated.
Send notifications to iOS app from backend server
There is no reliable way for the *application* to receive notifications if not running. Period.
The *user* can receive notifications fairly reliably if you use standard push notifications. These will appear on the device regardless of whether your app is running or not (assuming the user has elected to allow notifications for your app). But no code in your app is run unless the user taps the notification.