我尝试使用MERN堆栈创建一个项目，但遇到了这个错误。我已经添加了代理来创建JSON文件，但仍然没有成功。
错误：

GET http://localhost:5000/posts net::ERR_CONNECTION_REFUSED

我的操作：

export const getPosts = () => async (dispatch) => {
try {
    const {data} = await api.fetchPosts();

    dispatch({type: 'FETCH_ALL', payload: data});

} catch (error) {
    console.log(error.message);
}

// const action = {type: 'FETCH_ALL', payload: []}

// dispatch(action);
}

export const createPost = (post) => async (dispatch) => {
try {
    const {data} = await api.createPost(post);
    dispatch({type: 'CREATE', payload: data})
} catch (error) {
    console.log(error);        
}
}

我路线/岗位：

const router = express.Router();

router.get('/', getPosts);
router.post('/', createPost);

export default router;

服务器控制器：

export const getPosts = async (req, res) => {
        try {
            const postMessages = PostMessage.find();

            console.log(postMessages);

            res.status(200).json(postMessages);
        } catch (error) {
            res.status(404).json({message: error.message});
        }
    }

    export const createPost = async (req, res) => {
        const post = req.body;

        const newPost = new PostMessage(post);
        try {
            await newPost.save();

            res.status(201).json(newPost);

        } catch (error) {
            res.status(409).json({message: error.message});
        }
    }

服务器索引.js：

const app = express();

    //MIDDLEWARE

    app.use(bodyParser.json({limit: "30mb", extended: true}));
    app.use(bodyParser.urlencoded({limit: "30mb", extended: true}));
    app.use(cors());

    app.use('/posts', postRoutes);

    
    const PORT = process.env.PORT || 5000;

    mongoose.connect(CONNECTION_URL, {useNewUrlParser:true, useUnifiedTopology: true}) 
        .then(()=> app.listen(PORT, () => console.log('Server running on port:', PORT)))
        .catch((error)=> console.log(error.message));

    mongoose.set('useFindAndModify', false);

客户端API索引：

const url = 'http://localhost:5000/posts';

    export const fetchPosts = () => axios.get(url);
    export const createPost = (newPost) => axios.post(url, newPost)

client.json:

{
  "name": "osteoft",
  "version": "0.1.0",
  "private": true,
  "proxy": "http://localhost:5000",
  "dependencies": {
    "@material-ui/core": "^4.11.2",
    "@testing-library/jest-dom": "^5.11.4",
    "@testing-library/react": "^11.1.0",
    "@testing-library/user-event": "^12.1.10",
    "axios": "^0.21.1",
    "react": "^17.0.1",
    "react-dom": "^17.0.1",
    "react-file-base64": "^1.0.3",
    "react-redux": "^7.2.2",
    "react-scripts": "4.0.1",
    "redux": "^4.0.5",
    "redux-thunk": "^2.3.0",
    "web-vitals": "^0.2.4"
  },

尝试配置连接时是否缺少了什么？