React+Node.js注册/登录遇Network request failed及404错误求助

用React开发前端应用、Node.js搭建后端，注册或登录时持续遭遇相同的网络错误TypeError: Network request failed。Postman测试完全正常，说明后端、数据库及前端传值逻辑无问题，但浏览器提示：

"register:1 Failed to load resource: the server responded with a status of 404 (Not Found)"

SignUpScreen.js

function SignUpScreen(props) {

    const navigation = useNavigation();

    const navigateToSignIn = () => {
        navigation.navigate('Sign In');
      };

        const handleRegister = async () => {
            console.log('Start handleRegister');
            try {
                const response = await fetch('http://localhost/register', {
                    method: 'POST',
                    headers: {
                        'Content-Type': 'application/json',
                    },
                    body: JSON.stringify({  Email, password }),
                });

                console.log('After fetch'); 

                const data = await response.json();
        };

Backend code

app.post('/register', async (req, res) => {
    try {
        const { email, password } = req.body;
        
        const saltRounds = 10;
        const hashedPassword = await bcrypt.hash(password, saltRounds);


        const user = { email, password: hashedPassword };
        const insertUserQuery = 'INSERT INTO users (email, password) VALUES (?, ?)';

});

已尝试以下方案但未解决：

• 将“localhost”替换为IP地址
• 使用CORS
• 在Android清单文件android/app/src/main/AndroidManifest.xml中添加android:usesCleartextTraffic="true"
• 更换不同物理设备

内容的提问来源于stack exchange，提问作者steez