Heroku build failure when deploying Node.js/React app

I'm working on a React/Node app (using create-react-app) and trying to deploy it using Heroku. When we try to deploy on Heroku, we get the following error about react-scripts: sh: 1: react-scripts: not found.

Edit: looking at the full logs, it seems that Heroku successfully installed the node packages but for some reason it can't find react-scripts.

We've tried referring to similar issues on here but haven't had any luck finding a solution. Has anyone else ran into this and found a solution or know what might be causing?

Here's the full Heroku log and package.json files are below for reference:

-----> Building on the Heroku-20 stack
-----> Using buildpacks:
       1. heroku/nodejs
       2. mars/create-react-app
-----> Node.js app detected
       
-----> Creating runtime environment
       
       NPM_CONFIG_LOGLEVEL=error
       NODE_VERBOSE=false
       NODE_ENV=production
       NODE_MODULES_CACHE=true
       
-----> Installing binaries
       engines.node (package.json):  16.x
       engines.npm (package.json):   unspecified (use default)
       
       Resolving node version 16.x...
       Downloading and installing node 16.15.1...
       Using default npm version: 8.11.0
       
-----> Installing dependencies
       Installing node modules
       
       added 203 packages, and audited 204 packages in 12s
       
       58 packages are looking for funding
         run `npm fund` for details
       
       found 0 vulnerabilities
       
-----> Build
       Running heroku-postbuild
       
       > [email protected] heroku-postbuild
       > cd client && npm run build
       
       
       > [email protected] build
       > react-scripts build
       
sh: 1: react-scripts: not found
-----> Build failed
       
       We're sorry this build is failing! You can troubleshoot common issues here:
       https://devcenter.heroku.com/articles/troubleshooting-node-deploys
       
       If you're stuck, please submit a ticket so we can help:
       https://help.heroku.com/
       
       Love,
       Heroku
       
 !     Push rejected, failed to compile Node.js app.
 !     Push failed

Here are the package.json files for the app:

Root:

{
  "name": "pool-chem-calculator",
  "version": "1.0.0",
  "description": "Calculator that calculates pool water chemistry based off values in a form",
  "main": "server/server.js",
  "scripts": {
    "start": "if-env NODE_ENV=production && npm run start:prod || npm run start:dev",
    "start:prod": "cd server && npm start",
    "start:dev": "concurrently \"cd server && npm run dev\" \"cd client && npm start\"",
    "test": "cd client && npm run test",
    "lint": "npx eslint client/src",
    "heroku-postbuild": "cd client && npm run build"
  },
  "repository": {
    "type": "git",
    "url": "git+https://github.com/pschlafley/Pool-Chem-Calculator.git"
  },
  "author": "Peyton Schlafley, Tom Chestnut",
  "license": "MIT",
  "bugs": {
    "url": "https://github.com/pschlafley/Pool-Chem-Calculator/issues"
  },
  "homepage": "https://github.com/pschlafley/Pool-Chem-Calculator#readme",
  "devDependencies": {
    "concurrently": "^7.2.0",
    "eslint": "^7.11.0",
    "eslint-config-prettier": "^8.3.0",
    "eslint-plugin-react": "^7.28.0",
    "prettier": "^2.5.1"
  },
  "dependencies": {
    "if-env": "^1.0.4"
  },
  "engines": {
    "node": "16.x"
  }
}

Client:

{
  "name": "client",
  "version": "0.1.0",
  "private": true,
  "proxy": "http://localhost:3001",
  "type": "module",
  "dependencies": {
    "@apollo/client": "^3.6.2",
    "@emotion/react": "^11.7.1",
    "@emotion/styled": "^11.6.0",
    "@mui/material": "^5.3.0",
    "@testing-library/jest-dom": "^5.16.1",
    "@testing-library/react": "^11.2.7",
    "@testing-library/user-event": "^12.8.3",
    "formik": "^2.2.9",
    "graphql": "^16.5.0",
    "jwt-decode": "^3.1.2",
    "react": "^17.0.2",
    "react-dom": "^17.0.2",
    "react-router-dom": "^6.2.1",
    "react-scripts": "4.0.3",
    "web-vitals": "^1.1.2",
    "yup": "^0.32.11",
    "react-device-detect": "^2.1.2"
  },
  "scripts": {
    "start": "react-scripts start",
    "build": "react-scripts build",
    "test": "react-scripts test",
    "eject": "react-scripts eject"
  },
  "eslintConfig": {
    "extends": [
      "react-app",
      "react-app/jest"
    ]
  },
  "browserslist": {
    "production": [
      ">0.2%",
      "not dead",
      "not op_mini all"
    ],
    "development": [
      "last 1 chrome version",
      "last 1 firefox version",
      "last 1 safari version"
    ]
  }
}

Server:

{
  "name": "server",
  "version": "1.0.0",
  "description": "",
  "main": "server.js",
  "type": "module",
  "scripts": {
    "start": "node server.js",
    "dev": "nodemon server.js"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    "apollo-server-express": "^3.6.4",
    "bcrypt": "^5.0.1",
    "express": "^4.17.3",
    "graphql": "^16.3.0",
    "jsonwebtoken": "^8.5.1",
    "mongoose": "^6.2.7"
  },
  "devDependencies": {
    "nodemon": "^2.0.15"
  }
}