Timer not running when the app is in background

Question

i have a timer in swift:

private var timer: Timer?


    @objc
private func startBreakTime() {
    var count = 90
    self.breakTimeButton.isEnabled = false
    self.timer = Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) { [weak self] timer in
        guard let self = self else {
            timer.invalidate()
            return
        }
        
        count -= 1
        self.timerLabel.text = String(format: "%02d:%02d", count / 60, count % 60)
        
        if count == 0 {
            self.cancelBreakTimeForCountdown(timer: timer)
            self.counterFor += 1
            self.handleSeriesMessage()
            self.sendNotification()
            AudioServicesPlaySystemSound(SystemSoundID(kSystemSoundID_Vibrate))
        }
    }
}

When the interval reaches 0, the user should receive a notification, even if they are using another app. My problem is that my timer and the cell phone are not running together. For testing, I put a timer running, and when it reached 0, mine is still at 55 sec. How can I make my timer keep running, even with the app minimized?

I need to send notification, precisely 1:30 after he touches the button, even if he minimize

I have tried to sync my notification with my timer, but i dont know how