sh: mix: command not found / npm ERR!

前提・実現したいこと　

Laravelアプリに Vue を反映させるため、npm run devを実行したいのですが、噛み合わないパッケージをインストールしたせいか、また、慌てて npm のコマンドを実行しまくったせいか、どんな方法を試してみても上手くいきません。
もし何か思いつく方がいらっしゃれば教えて頂きたいです。

発生している問題

sh: mix: command not found
npm ERR! code ELIFECYCLE
npm ERR! syscall spawn
npm ERR! file sh
npm ERR! errno ENOENT
npm ERR! @ development: `mix`
npm ERR! spawn ENOENT
npm ERR! 
npm ERR! Failed at the @ development script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /Users/ユーザー名/.npm/_logs/2021-06-13T~Z-debug.log
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! @ dev: `npm run development`
npm ERR! Exit status 1
npm ERR! 
npm ERR! Failed at the @ dev script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /Users/ユーザー名/.npm/_logs/2021-06-13T~Z-debug.log

該当のソースコード

packagejson
1{
2    "private": true,
3    "scripts": {
4        "heroku-postbuild": "npm run prod",
5        "dev": "npm run development",
6        "development": "mix",
7        "watch": "mix watch",
8        "watch-poll": "mix watch -- --watch-options-poll=1000",
9        "hot": "mix watch --hot",
10        "prod": "npm run production",
11        "production": "mix --production"
12    },
13    "devDependencies": {
14        "@johmun/vue-tags-input": "^2.1.0",
15        "axios": "^0.19",
16        "cross-env": "^5.1",
17        "laravel-mix": "^4.0.7",
18        "lodash": "^4.17.13",
19        "resolve-url-loader": "^2.3.1",
20        "sass": "^1.15.2",
21        "sass-loader": "^7.1.0",
22        "vue": "^2.6.11",
23        "vue-template-compiler": "^2.6.11"
24    }
25}

webpackmixjs
1const mix = require('laravel-mix');
2
3/*
4 |--------------------------------------------------------------------------
5 | Mix Asset Management
6 |--------------------------------------------------------------------------
7 |
8 | Mix provides a clean, fluent API for defining some Webpack build steps
9 | for your Laravel application. By default, we are compiling the Sass
10 | file for the application as well as bundling up all the JS files.
11 |
12 */
13
14mix.js('resources/js/app.js', 'public/js')
15  .sass('resources/sass/app.scss', 'public/css')
16  .version();
17