tsc: not found error in heroku despite trying everything

I am trying to deploy a simple nodejs app to heroku but getting the above error. Tried solving it based on the available answers here, but nothing seems to work. Here's what I have tried already:

1. Installed typescript buildpack on dyno heroku buildpacks: heroku/nodejs zidizei/typescript
2. My package.json has typescript in devDependencies, and scripts has tsc in the build argument

  ...
  "main": "index.js",
  "dependencies": {
    "cors": "^2.8.5",
    "express": "^4.18.1",
    "rimraf": "^5.0.5",
  },
  "devDependencies": {
    "@types/express": "^4.17.14",
    "@types/node": "^18.11.0"
    "nodemon": "^2.0.19",
    "ts-node": "^10.9.1",
    "typescript": "^4.7.4"
  },
  "scripts": {
    "start": "node build/server.js",
    "postinstall": "tsc",
    "dev": "nodemon server.ts",
    "start:server": "ts-node server.ts",
    "test": "echo \"Error: no test specified\" && exit 1"
  }
...

3. My tsconfig.json also matches pretty much with the answer that I've seen here

{
   "ts-node": {
   "compilerOptions": {
     "module": "commonjs"
   }
 },
 "compilerOptions": {
   "module": "commonjs",
   "esModuleInterop": true,
   "target": "es6",
   "rootDir": "./",
   "outDir": "./build",
   "strict": true,
   "experimentalDecorators": true,
   "emitDecoratorMetadata": true,
   "strictPropertyInitialization": false,
   "moduleResolution":"node",
   "skipLibCheck": true
 },
 "files": [ "./utils/index.d.ts" ]
}

Error I am getting on the build step:

-----> TypeScript app detected
-----> Creating build environment
-----> Installing development dependencies
       Installing development node modules (npm)
       npm WARN invalid config only="dev" set in command line options
       npm WARN invalid config Must be one of: null, prod, production
       
       > rmr@1.0.0 postinstall
       > npm run build
       
       
       > rmr@1.0.0 build
       > tsc
       
       sh: 1: tsc: not found
       npm notice
       npm notice New minor version of npm available! 10.1.0 -> 10.2.3
       npm notice Changelog: <https://github.com/npm/cli/releases/tag/v10.2.3>
       npm notice Run `npm install -g npm@10.2.3` to update!
       npm notice
       npm ERR! code 127
       npm ERR! path /tmp/build_5663ceba
       npm ERR! command failed
       npm ERR! command sh -c npm run build

Exhausted all ideas about what I might be doing wrong and looking to get enlightened on the same. Any other things I should try?

Thanks in advance!

Got it working by putting tsc into build instead of postinstall, as heroku calls npm start build. At postinstall stage, it seems, devDependencies are no longer accessible.

...
  "scripts": {
    "start": "node build/server.js",
    "build": "tsc",
    "dev": "nodemon server.ts",
    "start:server": "ts-node server.ts",
    "test": "echo \"Error: no test specified\" && exit 1"
  }