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
{
    "private": true,
    "scripts": {
        "heroku-postbuild": "npm run prod",
        "dev": "npm run development",
        "development": "mix",
        "watch": "mix watch",
        "watch-poll": "mix watch -- --watch-options-poll=1000",
        "hot": "mix watch --hot",
        "prod": "npm run production",
        "production": "mix --production"
    },
    "devDependencies": {
        "@johmun/vue-tags-input": "^2.1.0",
        "axios": "^0.19",
        "cross-env": "^5.1",
        "laravel-mix": "^4.0.7",
        "lodash": "^4.17.13",
        "resolve-url-loader": "^2.3.1",
        "sass": "^1.15.2",
        "sass-loader": "^7.1.0",
        "vue": "^2.6.11",
        "vue-template-compiler": "^2.6.11"
    }
}

webpackmixjs
const mix = require('laravel-mix');

/*
 |--------------------------------------------------------------------------
 | Mix Asset Management
 |--------------------------------------------------------------------------
 |
 | Mix provides a clean, fluent API for defining some Webpack build steps
 | for your Laravel application. By default, we are compiling the Sass
 | file for the application as well as bundling up all the JS files.
 |
 */

mix.js('resources/js/app.js', 'public/js')
  .sass('resources/sass/app.scss', 'public/css')
  .version();