Node.js express server在生产路线上返回405

我第一次构建了一个express实例，我遇到了一个问题，所有东西都在本地工作，但部署后向路由发送post请求时，路由响应：

加载资源失败：服务器响应状态为405 （不允许）

Ive包括以下相关代码：

server/index.js

const express = require('express');
const bodyParser = require('body-parser')
const path = require('path');
const app = express();
app.use(express.static(path.join(__dirname, 'build')));
const routes = require('./routes')(express)
require('./db')

// parse application/x-www-form-urlencoded
app.use(bodyParser.urlencoded({ extended: false }))

// parse application/json
app.use(bodyParser.json())

app.get('/', function (req, res) {
  res.sendFile(path.join(__dirname, 'build', 'index.html'));
});

app.listen(process.env.PORT || 8080);

app.use('/', routes);

routes/index.js

var mongoose = require("mongoose");


const randomId = require('random-id');

const Submissions = require('../api/Submissions')


// routes/index.js
module.exports = (express) => {
  // Create express Router
  var router = express.Router();


  // add routes
  router.route('/submission')
    .post((req, res) => {

        let newSubmission = new Submissions(req.body);
        newSubmission._id = randomId(17, 'aA0');
        // Save the new model instance, passing a callback
        newSubmission.save(function(err,response) {
          if (err) {
            console.log(err)
          } else {
             res.setHeader('Content-Type', 'application/json');
             res.json({'success':true})
          }
          
          // saved!
        })
       
    });

  return router;
}

client.js

let submission = {
        name: this.state.newSubmission.name.trim(),
        body: this.state.newSubmission.body.trim(),
        email: this.state.newSubmission.email.trim(),
    };
    const requestOptions = {
        method: "POST",
        headers: { "Content-Type": "application/json" },
        body: JSON.stringify(submission),
    };
fetch("/submission", requestOptions)
        .then((response) =>
            response.json().then((data) => ({
                data: data,
                status: response.status,
            }))
        )
        .then((res) => {
            
            if (!res.data.success) {
                notifier.warning('Failed to submit');
            } else {
                notifier.success('Submission successful');
            }
        });