我有一个React/Node应用程序，它使用Axios发布到MongoDB Atlas。在本地，该应用程序可以成功调用，但在Heroku上部署后，我在控制台中收到以下错误消息：
POST http：//本地主机网络：：错误连接拒绝;未捕获（承诺中）o {消息：'网络错误'，名称：'AxiosError'，代码：错误_网络
React前端：

const handleClick = (event) => {
    event.preventDefault();
    const newConnection = {
        firstName: input.firstName, 
        lastName: input.lastName,
        email: input.email,
        comments: input.comments,
        date: new Date()
    }
    axios.post('http://localhost:3001/create', newConnection)
    
    window.alert("Thank you! We will be in touch soon.")
}

后端路由：

const express = require("express");
const router = express.Router();
const Connection = require("../models/connectionModel");
    
router.route("/create").post((req, res) => {
    const firstName = req.body.firstName;
    const lastName = req.body.lastName;
    const email = req.body.email;
    const comments = req.body.comments;
    const date = req.body.date;
    const newConnection = new Connection({
        firstName, 
        lastName,
        email,
        comments,
        date
    });

    newConnection.save();
})

module.exports = router;

后端服务器：

const express = require('express');
const app = express();
const cors = require('cors');
const mongoose = require('mongoose');
const path = require('path'); 
const port = process.env.PORT || 3001;

app.use(cors());
app.use(express.json());
app.use(express.static(path.resolve(__dirname, "./frontend/build")));

if (process.env.NODE_ENV !== 'production') {
    require('dotenv').config();
}

mongoose.connect(process.env.MONGODB_URI);

app.use("/", require("./routes/connectionRoute"));

app.listen(port, function() {
    console.log('express server is running on port 3001')
})

在搜索了Web以寻找解决方案后，我确认Express服务器正在端口3001上运行，并且启用了CORS。可能是我在www.example.com请求中使用的URL有问题，但我不确定如何继续。axios.post request, but I'm unsure how to proceed.
任何帮助将不胜感激!