Setting up the Frontend on my Shopify App

I am trying to set up a Shopify App using the Shopify PHP App Template.
Here is a link to it so you can take a look: GitHub - Shopify/shopify-app-template-php

I’ve followed all the steps and set up my app to use the TOML file with an NGROK Tunnel URL. It’s working properly because I can see network requests in the Shopify admin of my test store trying to access the “/” route on the app.

Correct me if I’m wrong but I’m pretty sure that the root route of my app (“/”) is supposed to be inside of the frontend on my app. To my current understanding I’m supposed to have that route and the /exitiframe route in my frontend and am supposed to make requests to my Laravel backend with it.

Assuming all that is correct, I’m having an issue with setting up the frontend of my app. I tried running these 2 commands but I can’t get the frontend to build

yarn build --client-id=[API_KEY]
yarn run dev

Also keep in mind that the yarn run dev command has been updated to use my NGROK Tunnel URL like this:

"shopify app dev --tunnel-url=https://workable-vertically-rattler.ngrok-free.app:8000"

Lastly I have made sure that I followed all the instructions in the Readme.md and I have updated my TOML file, auth callback urls and app scopes in my partner dashboard.

How do I get the frontend of my app to build so I can make sure that everything has been embedded properly.