Notification not sending

Hello There!, I'm currently working on an App with an implemented timer. It was initially planned, that the User will get a notification when the timer ends. Everything works fine until the timer ends and the phone doesn't gets any notification... This is my code:

import SwiftUI
import Combine
import UserNotifications

struct TimerView: View { @State private var timeRemaining: TimeInterval @State private var timerActive = false @Binding var studyTime: Int @Binding var selectedExam: Exam

init(studyTime: Binding<Int>, selectedExam: Binding<Exam>) {
    _studyTime = studyTime
    _selectedExam = selectedExam
    _timeRemaining = State(initialValue: TimeInterval(studyTime.wrappedValue * 60))
}

var body: some View {
    VStack {
        ZStack {
            Circle()
                .trim(from: 0, to: CGFloat(timeRemaining / (TimeInterval(studyTime * 60))))
                .stroke(Color.purple, lineWidth: 15)
                .rotationEffect(.degrees(-90))
                .animation(.linear(duration: 1))
                .padding(40)
            
            Text("\(timeRemaining.formattedTime)")
                .font(.system(size: 50))
        }
        
        Button(action: {
            self.timerActive.toggle()
        }) {
            Text(timerActive ? "Stop" : "Start")
                .font(.title)
                .padding()
        }
        .foregroundColor(.white)
        .background(timerActive ? Color.red : Color.green)
        .cornerRadius(10)
        .padding()
    }
    .onReceive(timer) { _ in
        guard self.timerActive else { return }
        if self.timeRemaining > 0 {
            self.timeRemaining -= 1
        } else {
            self.timerActive = false
            sendNotification()
        }
        print("Time Remaining: \(self.timeRemaining)")
    }
    .navigationTitle($selectedExam.wrappedValue.subject)
    .navigationBarBackButtonHidden(true)
    .onDisappear {
        // Actions if the timer View disappears
    }
}

var timer: AnyPublisher<Date, Never> {
    Timer.TimerPublisher(interval: 1.0, runLoop: .main, mode: .default)
        .autoconnect()
        .eraseToAnyPublisher()
}

func sendNotification() {
    let content = UNMutableNotificationContent()
    content.title = "Lernzeit vorbei"
    content.body = "Deine Lernzeit für \(selectedExam.subject) ist abgelaufen!"
    content.sound = UNNotificationSound.default
    
    let trigger = UNTimeIntervalNotificationTrigger(timeInterval: 1, repeats: false)
    let request = UNNotificationRequest(identifier: "timerNotification", content: content, trigger: trigger)
    
    UNUserNotificationCenter.current().add(request) { error in
        if let error = error {
            print("Fehler beim Hinzufügen der Benachrichtigung zur Warteschlange: \(error.localizedDescription)")
        } else {
            print("Benachrichtigung zur Warteschlange hinzugefügt")
        }
    }
}

}

extension TimeInterval { var formattedTime: String { let minutes = Int(self) / 60 % 60 let seconds = Int(self) % 60 return String(format: "%02i:%02i", minutes, seconds) } }

I looked it up and the app is allowed to send every type of notification... (this is initialized in another part of the code)