Where to retrieve Live activity update token that was started with ActivityKit push notifications using push-to-start token?

I can successfully start a Live Activity using push-to-start token, but in order to update the Live Activity i need another token as stated in the docs:

While the system starts the new Live Activity and wakes up your app, you receive the push token you use for updates.

When the app is open, i can retrieve this update token and successfully update the Live Activity using this example code:

func observeActivityPushToken() {
        Task {
            for await activityData in Activity<LiveActivityAttributes>.activityUpdates {
                Task {
                    for await tokenData in activityData.pushTokenUpdates {
                        let token = tokenData.map { String(format: "%02x", $0) }.joined()
                        print("Push token: \(token)")
                    }
                }
            }
        }
    }

But when the app is closed, how/where do i manage to get this update token and send it to the server "when the system wakes up the app"?