Heroku typescript deployment issue - node.js

Question

I am trying to deploy a nodejs application (which also uses typeORM) written in typescript to heroku.
My package.json devDependencies look like the following:
"devDependencies": {
"#types/cors": "^2.8.9",
"#types/node": "^8.10.66",
"nodemon": "^2.0.6",
"ts-node": "3.3.0",
"typescript": "3.3.3333"
},
and my scripts section look like so:
"scripts": {
"start": "node build/server.js",
"build": "tsc",
"postinstall": "npm run build",
"dev": "nodemon --exec ts-node src/server.ts"
}
I've set build to "tsc" so that Heroku compiles the typescript and specified the files to go inside the build folder, however when starting the server and running the tail log using heroku logs --tail, it seems to be trying to use my .ts files and it gives the error like below:
2021-01-03T22:30:28.445473+00:00 app[web.1]: Error: /app/src/entities/User.ts:1
2021-01-03T22:30:28.445474+00:00 app[web.1]: import { Person } from "./Person";
2021-01-03T22:30:28.445475+00:00 app[web.1]: ^^^^^^
2021-01-03T22:30:28.445475+00:00 app[web.1]:
2021-01-03T22:30:28.445479+00:00 app[web.1]: SyntaxError: Cannot use import statement outside a module
2021-01-03T22:30:28.445480+00:00 app[web.1]: at wrapSafe (internal/modules/cjs/loader.js:915:16)
2021-01-03T22:30:28.445480+00:00 app[web.1]: at Module._compile (internal/modules/cjs/loader.js:963:27)
2021-01-03T22:30:28.445481+00:00 app[web.1]: at Object.Module._extensions..js (internal/modules/cjs/loader.js:1027:10)
2021-01-03T22:30:28.445482+00:00 app[web.1]: at Module.load (internal/modules/cjs/loader.js:863:32)
2021-01-03T22:30:28.445482+00:00 app[web.1]: at Function.Module._load (internal/modules/cjs/loader.js:708:14)
2021-01-03T22:30:28.445483+00:00 app[web.1]: at Module.require (internal/modules/cjs/loader.js:887:19)
2021-01-03T22:30:28.445483+00:00 app[web.1]: at require (internal/modules/cjs/helpers.js:74:18)
2021-01-03T22:30:28.445484+00:00 app[web.1]: at /app/node_modules/typeorm/util/DirectoryExportedClassesLoader.js:41:39
2021-01-03T22:30:28.445484+00:00 app[web.1]: at Array.map (<anonymous>)
2021-01-03T22:30:28.445485+00:00 app[web.1]: at Object.importClassesFromDirectories (/app/node_modules/typeorm/util/DirectoryExportedClassesLoader.js:41:10)
2021-01-03T22:30:28.445704+00:00 app[web.1]: Cannot use import statement outside a module
Also note that i don't have a Procfile as it handles it by default.
Is there some other information i am missing to include?
Thanks