MERN app depolying to Heroku - package.json not found - node.js

Question

I'm trying to use the Heroku CLI to get a MERN app online. The app works perfectly locally but when I try to use git to push the app onto Heroku I get the following error message:
remote: Running heroku-postbuild
remote:
remote: > exercise-logger#1.0.0 heroku-postbuild /tmp/build_431a136c
remote: > NPM_CONFIG_PRODUCTION=false npm install --prefix exercise-logger && npm run build --prefix exercise-logger
remote:
remote: up to date in 0.22s
remote: found 0 vulnerabilities
remote:
remote: npm ERR! code ENOENT
remote: npm ERR! syscall open
remote: npm ERR! path /tmp/build_431a136c/exercise-logger/package.json
remote: npm ERR! errno -2
remote: npm ERR! enoent ENOENT: no such file or directory, open '/tmp/build_431a136c/exercise-logger/package.json'
remote: npm ERR! enoent This is related to npm not being able to find a file.
remote: npm ERR! enoent
remote:
remote: npm ERR! A complete log of this run can be found in:
remote: npm ERR! /tmp/npmcache.yesMz/_logs/2021-05-30T17_32_30_947Z-debug.log
remote: npm ERR! code ELIFECYCLE
remote: npm ERR! errno 254
remote: npm ERR! exercise-logger#1.0.0 heroku-postbuild: `NPM_CONFIG_PRODUCTION=false npm install --prefix exercise-logger && npm run build --prefix exercise-logger`
remote: npm ERR! Exit status 254
remote: npm ERR!
remote: npm ERR! Failed at the exercise-logger#1.0.0 heroku-postbuild script.
remote: npm ERR! This is probably not a problem with npm. There is likely additional logging output above.
remote:
remote: npm ERR! A complete log of this run can be found in:
remote: npm ERR! /tmp/npmcache.yesMz/_logs/2021-05-30T17_32_30_973Z-debug.log
remote:
remote: -----> Build failed
remote:
remote: We're sorry this build is failing! You can troubleshoot common issues here:
remote: https://devcenter.heroku.com/articles/troubleshooting-node-deploys
remote:
remote: Some possible problems:
remote:
remote: - node_modules checked into source control
remote: https://devcenter.heroku.com/articles/node-best-practices#only-git-the-important-bits
remote:
remote: Love,
remote: Heroku
remote:
remote: ! Push rejected, failed to compile Node.js app.
remote:
remote: ! Push failed
remote: !
The thrust of it seems to be that it can't find the root package.json file, even though it's definitely there. In fact, here it is:
"name": "exercise-logger",
"version": "1.0.0",
"description": "",
"main": "server.js",
"dependencies": {
"axios": "^0.21.1",
"bcrypt": "^5.0.1",
"concurrently": "^6.0.2",
"config": "^3.3.6",
"cors": "^2.8.5",
"express": "^4.17.1",
"express-validator": "^6.10.0",
"jsonwebtoken": "^8.5.1",
"mongoose": "^5.12.3"
},
"devDependencies": {},
"scripts": {
"start": "node server.js",
"build": "cd client && npm run build",
"server": "nodemon server.js",
"client": "npm start --prefix client",
"clientinstall": "npm install --prefix client",
"dev": "concurrently \"npm run start\" \"npm run client\"",
"heroku-postbuild": "NPM_CONFIG_PRODUCTION=false npm install --prefix client && npm run build --prefix client"
},
"engines": {
"node": "14.x",
"npm": "6.x"
},
"author": "",
"license": "ISC"
}
I have tried what seems to be a common fix which is manually deleting the .git folder in the directory for the React app but doesn't seem to have fixed it.
The whole code is on Github here.
Can anyone help? I've been working on this project for quite a while so it's really frustrating to fall at the final hurdle like this. I've not really done anything like this before so not really sure where to start troubleshooting!
Thanks