I'm learning programming now so forgive me for any mistakes, I'll be grateful for any tips. I have an API that is hosted in the following domain ("api-myapp.com") and I'm trying from my localhost where I'm creating my front-end to post a form (which only logged in users can send) using axios , but the request takes a long time to complete and when it completes it returns the following error (No 'Access-Control-Allow-Origin' header is present on the requested resource.) (net::ERR_FAILED 504), I've tried some solutions I found on the internet but none seem to have worked, this is my code:

FrontEnd:

 try {
        const response = await axios.post('/alunos/', {
            nome,sobrenome,idade,sangue,varinha,patrono,house,sala,
        });
        toast.success('Cadastrado com sucesso');
        console.log(response);
    } catch (e) {
        console.log(e);
        const errors = get(e, 'response.data.errors', []);
        errors.map((error) => toast.error(error));
    }

When you logged in

 try {
    const response = yield call(axios.post, '/tokens', payload);
    yield put(actions.loginSuccess({ ...response.data }));
    axios.defaults.headers.Authorization = `Bearer ${response.data.token}`;
    toast.success('Login realizado com sucesso!');
    payload.navigate('/dashboard');
}

BackEnd

class App {
  constructor() {
    this.app = express();
    this.middlewares();
    this.routes();
  }

  middlewares() {
    this.app.use(cors({ origin: '*' }));
    this.app.use(helmet({ crossOriginResourcePolicy: false }));
    this.app.use(express.urlencoded({ extended: true }));
    this.app.use(express.json());
    this.app.use('/images/', express.static(resolve(__dirname, '..', 'uploads', 'images')));
  }

  routes() {
    this.app.use('/', homeRoutes);
    this.app.use('/prof', profRoutes);
    this.app.use('/tokens', tokenRoutes);
    this.app.use('/alunos', alunoRoutes);
    this.app.use('/casas', casaRoutes);
    this.app.use('/provas', provaRoutes);
    this.app.use('/materias', materiaRoutes);
    this.app.use('/salas', salaRoutes);
    this.app.use('/fotosAlunos', fotoAlunoRoutes);
    this.app.use('/fotosProf', fotoProfRoutes);
  }
}