Error when trying to containerize a Docker image - heroku

Question

I am working on a project and cant get past this error and google hasnt helped me much. Would someone be able to help me understand what to fix here?
The full repo you can find here: https://github.com/apatel544/good-eat-delivery-app
Ive tried deploying this to heroku and there was an error when I try pushing the heroku container up to the master heroku app. The above code snippets were what many posts said was the solution but now its giving my the error I pasted above.
My Dockerfile:
`
FROM node:14
#create app directory
RUN mkdir -p /usr/src/app
WORKDIR /usr/src/app
#installing dependencies
COPY package*.json /usr/src/app/
RUN npm install
#copying source files
COPY . /usr/src/app
#building app
RUN npm run build
#running the app
CMD "npm" "run" "start"
`
My Package.json (running node version 14.0.0 because the project is a bit dated)
{
"name": "restaurant-app",
"version": "0.1.0",
"private": true,
"scripts": {
"dev": "next dev",
"build": "next build",
"start": "next start -p $PORT"
},
"dependencies": {
"#apollo/client": "^3.2.4",
"#stripe/react-stripe-js": "^1.1.2",
"#stripe/stripe-js": "^1.10.0",
"axios": "^0.19.2",
"firebase": "^9.12.1",
"graphql": "^15.3.0",
"isomorphic-fetch": "^2.2.1",
"js-cookie": "^2.2.1",
"next": "^9.5.5",
"react": "16.14.0",
"react-dom": "16.14.0",
"reactstrap": "^8.6.0"
},
"description": "Exercise05 is full Shopping Cart with Stripe Billing",
"main": "index.js",
"author": "jrw#mit.edu",
"license": "MIT"
}
Error Message:
restaurant-app#0.1.0 start /usr/src/app
next start -p $PORT
(node:20) UnhandledPromiseRejectionWarning: Error: Option requires argument: -p (alias for --port)
at arg (/usr/src/app/node_modules/next/dist/compiled/arg/index.js:1:2174)
at nextStart (/usr/src/app/node_modules/next/dist/cli/next-start.js:4:84)
at /usr/src/app/node_modules/next/dist/bin/next:26:341
(Use node --trace-warnings ... to show where the warning was created)
(node:20) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag --unhandled-rejections=strict (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 1)
(node:20) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.