nodeサーバーで発生したエラーを解決したい。

前提・実現したいこと

現在、Node.js, Vue.jsを用いてamazonウェブサイトのクローンを作っています。
そこでルーティングを実装中の際に、以下のエラーがターミナルにて発生しました。

発生している問題・エラーメッセージ

[nodemon] 2.0.1
[nodemon] to restart at any time, enter `rs`
[nodemon] watching dir(s): *.*
[nodemon] watching extensions: js,mjs,json
[nodemon] starting `node server.js`
/Users/user/amazon/server/routes/product.js:14
router.post('/products', upload.single('photo'), async (req, res) => {
                                ^

TypeError: upload.single is not a function
    at Object.<anonymous> (/Users/user/amazon/server/routes/product.js:14:33)
    at Module._compile (internal/modules/cjs/loader.js:778:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:789:10)
    at Module.load (internal/modules/cjs/loader.js:653:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:593:12)
    at Function.Module._load (internal/modules/cjs/loader.js:585:3)
    at Module.require (internal/modules/cjs/loader.js:692:17)
    at require (internal/modules/cjs/helpers.js:25:18)
    at Object.<anonymous> (/Users/user/amazon/server/server.js:31:23)
    at Module._compile (internal/modules/cjs/loader.js:778:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:789:10)
    at Module.load (internal/modules/cjs/loader.js:653:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:593:12)
    at Function.Module._load (internal/modules/cjs/loader.js:585:3)
    at Function.Module.runMain (internal/modules/cjs/loader.js:831:12)
    at startup (internal/bootstrap/node.js:283:19)
[nodemon] app crashed - waiting for file changes before starting...

該当のソースコード

const router = require('express').Router()
const Product = require('../models/product')

const upload = require('../middlewares/upload-photo')
// POST request - create new product

// title: String,
//  description: String,
//  photo: String,
//  price: String,
//  stockQuantity: Number,
//  rating: [Number]

router.post('/products', upload.single('photo'), async (req, res) => {
  try {
    let product = new Product()
    product.title = req.body.title
    product.description = req.body.description
    product.photo = req.body.photo
    product.stockQuantity = req.body.stockQuantity

    await product.save() // async

    res.json({
      status: true,
      message: 'Successfully saved'
    })
  } catch(err) {
    res.status(500).json({
      success: false,
      message: err.message
    })
  }
})

// GET request - get all product



// GET request - get a single product


// PUT request - Update a single product





// DELETE request - delete a single product
module.exports = router

試したこと

こちらのサイトを参考に、ターミナルにて npm i を実行して再度、nodemon server.js を実行しましたが、解決には至りませんでした。

補足情報（package.json）

{
"name": "server.js",
"version": "1.0.0",
"description": "",
"main": "index.js",
"scripts": {
"test": "echo \"Error: no test specified\" && exit 1"
},
"author": "",
"license": "ISC",
"dependencies": {
"aws-sdk": "^2.580.0",
"body-parser": "^1.19.0",
"dotenv": "^8.2.0",
"express": "^4.17.1",
"mongodb": "^3.3.5",
"mongoose": "^5.7.12",
"morgan": "^1.9.1",
"multer": "^1.4.2",
"multer-s3": "^2.9.0",
"npm": "^6.13.1"
}
}