Spring Boot Service always null after @Autowire in JavaFX Controller Class

Question

I am currently developing an application that uses Spring Boot and JavaFX. I want to store email and password in H2 database. With a JUnit test I have already checked if the database is running and I have access to the Spring Boot repository. This works. However, I need to access the Spring Boot service from the JavaFX controller to be able to control the logic from the GUI and after I autowire the Spring Boot service in this class, a NullPointerException comes.

JavaFXController

@Component
@FxmlView("start.fxml")
@Service
public class JavaFXController {

    @FXML private Label startLabel;
    @FXML private Label settingsLabel;
    @FXML private TextField emailAmazonMerchOnDemand;
    @FXML private PasswordField passwordAmazonMerchOnDemand;

    private Stage stage;
    private Scene scene;

    @Autowired
    private AmazonMerchOnDemandService amazonMerchOnDemandService;

    @FXML
    public void openSettingsSceneFromStartScene() throws IOException {
        Parent root = FXMLLoader.load(getClass().getClassLoader().getResource("settings.fxml"));
        stage = (Stage)(startLabel.getScene().getWindow());
        scene = new Scene(root);
        stage.setScene(scene);
        stage.show();
    }

    @FXML
    public void saveLogins() {
        String emailAmazon = emailAmazonMerchOnDemand.getText();
        String passwordAmazon = passwordAmazonMerchOnDemand.getText();
        AmazonMerchOnDemand amazonMerchOnDemandLogin = new AmazonMerchOnDemand();
        amazonMerchOnDemandLogin.setId(1L);
        amazonMerchOnDemandLogin.setEmail(emailAmazon);
        amazonMerchOnDemandLogin.setPassword(passwordAmazon);
        amazonMerchOnDemandService.saveLogin(amazonMerchOnDemandLogin);
    }
}

JavaFXApplication

@SpringBootApplication
public class JavaFXApplication extends Application {
    private ConfigurableApplicationContext applicationContext;

    @Override
    public void init() throws Exception {
        String[] args = getParameters().getRaw().toArray(new String[0]);
        this.applicationContext = new SpringApplicationBuilder().sources(PrintOnDemandSellerViewApplication.class).run(args);
    }

    @Override
    public void start(Stage stage) throws Exception {
        FXMLLoader loader = new FXMLLoader();
        URL xmlUrl = getClass().getClassLoader().getResource("start.fxml");
        loader.setLocation(xmlUrl);
        loader.setController(applicationContext.getBean(JavaFXController.class));
        Parent root = loader.load();
        Scene scene = new Scene(root);
        stage.setScene(scene);
        stage.show();
    }

    @Override
    public void stop() throws Exception {
        this.applicationContext.close();
        Platform.exit();
    }
}

AmazonMerchOnDemandService

@Service
@Component
public class AmazonMerchOnDemandService {

    public static WebDriver driver;
    private static int amountOfSales;

    @Autowired
    private AmazonMerchOnDemandRepository amazonMerchOnDemandRepository;

    public void saveLogin(AmazonMerchOnDemand amazonMerchOnDemand) {
        amazonMerchOnDemandRepository.save(amazonMerchOnDemand);
    }

    public void chromeDriverSetUp() {
        System.setProperty("webdriver.chrome.driver", "C:\\Program Files (x86)\\chromedriver.exe");
        driver = new ChromeDriver();
        driver.manage().window().maximize();
    }

    public void login() {
        String email = amazonMerchOnDemandRepository.findById(1L).get().getEmail();
        System.out.println("Email: " + email);
        String password = amazonMerchOnDemandRepository.findById(1L).get().getPassword();
        System.out.println("Password: " + password);
}
}

AmazonMerchOnDemandRepository

@Repository
public interface AmazonMerchOnDemandRepository extends CrudRepository <AmazonMerchOnDemand, Long> {
}

PrintOnDemandSellerViewApplicationTests

@SpringBootTest(classes = JavaFXApplication.class)
class PrintOnDemandSellerViewApplicationTests {

    @Autowired
    private AmazonMerchOnDemandRepository amazonMerchOnDemandRepository;
    @Autowired
    private AmazonMerchOnDemandSampleData amazonMerchOnDemandSampleData;

    @BeforeEach
    public void setupData() {
        amazonMerchOnDemandSampleData.createAmazonMerchOnDemandLogin();
    }

    @Test
    public void testHasAmazonMerchOnDemandLoginRightPasswordAndRightEmail() {
        assertTrue(amazonMerchOnDemandRepository.existsById(1L));
        Optional<AmazonMerchOnDemand> amazonMerchOnDemandOptional = amazonMerchOnDemandRepository.findById(1L);
        assertFalse(amazonMerchOnDemandOptional.isEmpty());
        AmazonMerchOnDemand amazonMerchOnDemandLogin = amazonMerchOnDemandOptional.get();
        assertEquals("password", amazonMerchOnDemandLogin.getPassword());
        assertEquals("test@gmail.com", amazonMerchOnDemandLogin.getEmail());
    }

}

NullPointerException

Caused by: java.lang.reflect.InvocationTargetException
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:566)
    at com.sun.javafx.reflect.Trampoline.invoke(MethodUtil.java:77)
    at jdk.internal.reflect.GeneratedMethodAccessor37.invoke(Unknown Source)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:566)
    at javafx.base@19/com.sun.javafx.reflect.MethodUtil.invoke(MethodUtil.java:275)
    at javafx.fxml@19/com.sun.javafx.fxml.MethodHelper.invoke(MethodHelper.java:84)
    at javafx.fxml@19/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1854)
    ... 29 more
Caused by: java.lang.NullPointerException
    at com.example.printondemandsellerview.JavaFXController.saveLogins(JavaFXController.java:53)
    ... 40 more

I have tried several solutions from StackOverflow:

Dependency Injection in JavaFX Spring Data Autowire in FXML Controller

Unfortunately, none of the solutions could help me. Do you have any other suggestions as to what the problem might be?